Methods for plasma processing

ABSTRACT

Apparatus and method for plasma-based processing well suited for deposition, etching, or treatment of semiconductor, conductor or insulating films. Plasma generating units include one or more elongated electrodes on the processing side of a substrate and a neutral electrode proximate the opposite side of the substrate. Gases may be injected proximate a powered electrode which break down electrically and produce activated species that flow toward the substrate area. This gas then flows into an extended process region between powered electrodes and substrate, providing controlled and continuous reactivity with the substrate at high rates with efficient utilization of reactant feedstock. Gases are exhausted via passages between powered electrodes or electrode and divider.

CROSS REFERENCE

This application is a CONTINUATION of U.S. patent application Ser. No.14/253,206, filed Apr. 15, 2014, which is a CONTINUATION of U.S. patentapplication Ser. No. 12/832,934, filed Jul. 8, 2010, that in turn claimsthe benefit of U.S. Provisional Patent Application No. 61/224,047, filedJul. 8, 2009, and U.S. Provisional Patent Application No. 61/322,788,filed Apr. 9, 2010, each of which is incorporated herein by reference.

This application is also related to co-pending U.S. patent applicationSer. No. 12/832,947, filed Jul. 8, 2010, entitled “Plasma GeneratingUnits for Processing a Substrate”; U.S. patent application Ser. No.12/832,953, filed Jul. 8, 2010, entitled “Apparatus for PlasmaProcessing”; and International Patent Application No. PCT/US2010/041440,filed Jul. 8, 2010, entitled “Apparatus and Method for PlasmaProcessing”, each incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The field of the present invention relates to an apparatus and methodsfor plasma processing, and more particularly, to alternating currentinduced plasma processing for deposition, etching, or treatment ofsemiconductor, conductor or insulating films or carriers holding smallersubstrates, rectangular substrates, or continuous band substrates.

2. Background

The development of plasma enhanced processes for deposition, etching,cleaning, and surface treatments have been instrumental to maintain theprogress in many manufacturing industries, such as, integrated circuits(IC), liquid crystal display (LCD) screens, and photovoltaic (PV)panels.

Example reactors for plasma enhanced processing include parallel platecapacitive and microwave discharge reactors. Scaling reactors to processlarger substrates may increase manufacturing cost because of the need tooperate at lower power density and gas concentration per unit area tomaintain desired film properties and uniformity.

For the IC and LCD industries, the cost of scaling plasma enhancedprocesses to larger substrates has been offset partially by theincreased functionality per unit area (IC) and ability to charge ahigher price for more surface area (LCD). The PV panel industry, on theother hand, faces additional challenges in finding ways to directlyreduce manufacturing cost and energy use per unit area produced whilealso improving the deposition methods to produce panels with higherconversion efficiency of light to electrical energy. One method ofmanufacturing PV panels involves Plasma Enhanced Chemical Vapor (PECVD)deposition of silicon containing thin films.

However, bombardment by high-energy ions (>10 eV), formation of siliconparticles in the gas phase, and metal contamination are factors that cancontribute to defects in the deposited silicon films that reduce theefficiency of converting light to electrical energy. For many PECVDprocesses, it may be desired to achieve economical high rate deposition,uniformity over large area substrates (including at edges and corners oflarge rectangular substrates) and efficient feedgas utilization.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 shows cross-section view of a processing system with closelyspaced PGUs according to an example embodiment of the present invention.

FIG. 2 shows cross-section view of a processing system with individuallymounted PGUs according to an example embodiment of the presentinvention.

FIG. 3 shows a perspective illustration of the dimensional aspect ratiosof an example wide and narrow electrode in relation to the substrateposition.

FIGS. 4 a-l show schematic cross-section views of twelve example PGUconfigurations in accordance with example embodiments of the presentinvention.

FIG. 5 shows the cross sectional view, radio frequency (RF) or VHFsupply configuration and plasma regions of a symmetrical two electrodePGU according to an example embodiment.

FIG. 6 shows the uniform gas flow paths and example arrangement forapplications requiring multiple sources according to an exampleembodiment.

FIG. 7 shows the example arrangement of FIG. 6 with the addition ofdielectric shields or liners mounted to the electrodes with a narrow gapto the electrode body.

FIG. 8 illustrates an example gas injection feature that allows thecombination of two independent gas flow channels to be added as auniformly controlled distribution of added reactive gas to the substrateprocess region in accordance with an example embodiment.

FIG. 9 shows an alternative PGU embodiment that accomplishes gas flow inonly one direction along the substrate surface.

FIG. 10 shows the uniform gas flow paths and an example for applicationsrequiring multiple sources according to an example embodiment.

FIG. 11 shows an alternative PGU embodiment utilizing a non-rectangularelectrode cross-section.

FIG. 12 shows a close up view of the gaps regions between electrodes andbetween electrodes and substrate in example embodiments.

FIG. 13 shows a cross section of a reactor chamber according to anexample embodiment having five PGUs in which the first two PGUs performa process using gases A, B, and C, the third PGU uses only inert gasesHe and Ar to provide separation, and the last two PGUs use gases D, E, Fto perform a different process.

FIG. 14 shows a cross section of a reactor chamber according to anexample embodiment having a pedestal which provides multiple smallseparate apertures for gas injection and pumping between itself and thesubstrate.

FIG. 15 shows a cross section of a substrate support and substrateaccording to an example embodiment where there is gas injection andpumping from the substrate support from baffled openings.

FIG. 16 shows a cross section of a substrate support and substrateaccording to an example embodiment where the support has baffled gasinjectors and has pumping apertures that are filled by porousgas-conductive and electrically conductive material preventing electricfields from penetrating into the larger diameter channels used forpumping.

FIG. 17 shows a cross section of a reactor chamber according to anexample embodiment wherein plasma formation is by inductive couplingusing multiple turns of a conductor in which AC current generates achanging magnetic field in the direction of gas flow resulting in aninduced electric field parallel to the long dimension of the PGU and thedirection of current flow in the turns of the coils.

FIG. 18 shows an electrical circuit model of the electrodes with linersillustrating delivery of RF or VHF power to dual electrodes by a singlepower supply using an inductive splitter according to an exampleembodiment.

FIG. 19 shows electrodes having recesses in the middle where gasdelivery is both from the recesses and the other substrate-facingsurfaces of the electrodes according to an example embodiment.

FIG. 20 shows a multiple electrode configuration according to an exampleembodiment where gas is injected only toward the substrate at the bottomof the electrodes, and each has multi-segment gas injection manifold.

FIG. 21 a shows a system according to an example embodiment where gas isinjected and dense plasma is formed between the electrodes, as well asbetween electrodes and substrate.

FIG. 21 b shows a system according to an example embodiment wherein thegap between the electrodes is filled in part by a dielectric slab.

FIG. 22 shows a cross section view of multiple PGUs and a manifold usedfor pumping the exhaust from the processing plasma according to anexample embodiment.

FIG. 23 shows an example multi-layer structure that may be manufacturedusing example systems and methods according to example embodiments.

DETAILED DESCRIPTION

While the present invention is open to various modifications andalternative constructions, the embodiments shown in the drawings will bedescribed herein in detail. It is to be understood, however, there is nointention to limit the invention to the particular forms disclosed. Onthe contrary, it is intended that the invention cover all modifications,equivalences and alternative constructions falling within the spirit andscope of the invention as expressed in the appended claims.

Example embodiments include plasma generating units (PGUs) each of whichmay generate or sustain, or contribute to the generation or sustainingof, a plasma for plasma processing. In example embodiments, the PGUs mayinclude one or more elements to provide power to generate or sustain aplasma (or to contribute to generating or sustaining a plasma), to helpcontain and/or provide a return path for the electric current, and/or toguide or control gas flow of the plasma.

Thus, each PGU may generate a plasma in a region which is adjacentelements of that PGU as well as adjacent other plasma regions or part ofa larger plasma region. In either case, the plasma in this region may besubstantially controllable with the power provided to some elements ofthis PGU in example embodiments. In some embodiments, the elements maybe electrodes at lower frequencies (such as RF or even VHF frequencies)that couple power into the plasma mainly through displacementcurrents—capacitive coupling. In other embodiments, the coupling ofpower from the PGU into the plasma may be principally inductive wheresome elements of the PGU include one or more turns of a coil. Otherembodiments may use power in the UHF or microwave bands with coupling ofpower into the plasma as surface waves which are electromagnetic intheir nature. In any of these example embodiments, processing in thisregion may be substantially a product of the plasma generated by ACelectrical power injected via the PGU. Other embodiments may usecombinations of PGUs that couple power capacitively, inductively or bysurface waves. These are examples only and other embodiments may useother PGUs or combinations of PGUs.

Elements of a PGU may include, for example, one or more poweredelectrodes, grounded electrodes, neutral electrodes and/or floatingelectrodes, one or more dividers to guide or control gas flow and/or tohelp contain power, and/or one or more liners to protect the electrodesor other chamber surfaces (and which may also help guide or control gasflow). These and/or other elements may be used alone or in combinationto provide the desired plasma properties for processing, as furtherdescribed below. In some embodiments, processing occurs as a substrateis moved under one or more PGUs. In other embodiments, the substrate isstationary under a PGU or an array or other combination of PGUs. In yetother embodiments, the substrate may be stationary while a single PGU orarray or other combination of PGUs are moved.

Shown in FIG. 1 is a processing chamber, 100, according to an exampleembodiment which may contain one or more plasma generating units (PGUs).FIG. 1 shows an example embodiment of a chamber having three PGUs, shownas items 101, 102 and 103, that are closely spaced to one another. ThePGUs may be of the same type or have different configurations ofelectrode(s), divider(s) and/or other elements. As shown in FIG. 1, themultiple PGUs in this embodiment are closely spaced, so that there maybe plasma generated between elements of adjacent PGUs as well as betweenelements within each individual PGU. In some example embodiments, thegaps between adjacent PGUs may be less than the width of each PGU. Insome embodiments, the gap between adjacent PGUs may be less than abouttwice the gap between the powered electrodes and the substrate beingprocessed. In this example embodiment. AC current may flow between PGUsas well as within each PGU. In this embodiment, each PGU has at leastone electrode, one of which is powered, and may or may not have adivider or multiple dividers which are not grounded or powered. Exampleembodiments of each PGU may have at least one powered electrode and mayhave a plurality of powered electrodes. Example embodiments may alsohave one or more grounded electrodes. Inert gas may be supplied throughan inlet as shown at 104, to a distribution manifold 118 and 119 oneither side of the PGU assembly to prevent process gases from leavingthe chamber and prevent the entry of gases from the adjacent chamberinto the process region. In example embodiments, such gas purging at theentry and exit of the chamber may also help remove undesirable gasesfrom the substrates as they enter the chamber to avoid contamination ofthe processes within the chamber. AC power is provided by generators,105, 106 and 107, respectively to PGU 101, 102 and 103. Gas supplyinlets, 108, 110, and 112, and exhaust ports 109, 111, and 113 areprovided for PGU 101, 102 and 103 respectively. In this exampleembodiment, the substrate is moved laterally below the PGUs forprocessing. Substrate motion into and out of the processing chamber inthis embodiment is indicated by the arrow at 114. A conveyor, web orother moveable transport or carrier may be used to move the substratebelow the PGUs. A substrate support and neutral electrode, 115, may beconnected to ground through an impedance element, 120, which mayincorporate reactive and resistive elements as well as solid stateelectronic devices such as power diodes or varistors that may be usedfor sensing the plasma condition and assuring process stability andcorrectness. There are heater elements, 121, that may be incorporatedinto (or near) the pedestal, 115. Such elements may be resistive withinthe pedestal (as shown) or radiative and below the pedestal. Exhaustports 116 and 117 are provided to pump out the purge gases which aredelivered to the substrate region by purge manifolds, 118 and 119. Insome embodiments with multiple PGUs, the PGUs are grouped closely withgaps between adjacent elements of neighboring PGUs that are less thantwice the gap between the substrate and the powered electrode(s) of oneor both of those PGUs.

In example embodiments, the PGUs may be arranged so that the long sidesof adjacent elements of neighboring PGUs are approximately parallel andnarrowly spaced along the direction of substrate motion.

Shown in FIG. 2 is another embodiment of a processing chamber withmultiple PGUs that are more widely spaced or may be isolated compared tothe previously described embodiment in FIG. 1. In this case each PGU mayhave at least two electrodes, and may or may not have a divider ormultiple dividers (which may not be grounded or powered). There may insome embodiments be only one PGU within a processing chamber. Chamber200 is shown with three PGUs. In this case very little AC current mayflow between different PGUs in addition to that within any PGU. The PGUsshown as items 201, 202 and 203 may be of the same type or havedifferent configurations of electrode(s) or divider(s). As shown, themultiple PGUs are not closely spaced, with gaps that may be less thanthe PGU width so that there may be little or no plasma generated betweenelements of adjacent PGUs.

Inert gas may as well be supplied, 204, to distribution manifolds 221and 222 on either side of the PGU assembly to prevent process gases fromleaving the chamber. In some embodiments AC power is provided bygenerators, 205 and 206 to PGU 201; generators 207 and 208 to PGU 202,and generators 209 and 210 to PGU 203. In other embodiments a singlegenerator may also be adequate for supplying all powered electrodeswithin one or more of the PGUs. Gas supplies, 211, 213, and 215, andexhausts 212, 214, and 216 are provided for PGU 201, 202 and 203respectively. Substrate motion into and out of the processing chamber isindicated as 217. The substrate support and neutral electrode, 218, maybe connected to ground through an impedance element, 223, which mayincorporate reactive and resistive elements as well as solid stateelectronic devices such as power diodes or varistors that may be usedfor sensing the plasma condition and assuring process stability andcorrectness. There may be a heater element, 224, which either conductsheat to the pedestal, 218, from within the pedestal as shown or radiatesheat to the pedestal and substrate from below and near the pedestal.Exhausts 219 and 220 are provided to pump out the purge gases which aredelivered to the substrate region by purge manifolds, 221 and 222.

Example elements within a PGU shown in FIG. 3 are generally proportionedand shaped to process substrates uniformly. The lengths of an electrode,301, or divider, 302, within a PGU, as shown in FIG. 3, may be longerthan the dimension of the substrate, 303, parallel to such length.Electrode or divider length may also be much greater than their heights,311 and 312, in the direction perpendicular to the substrate, or theirwidths, 321 and 322, in the direction parallel to the substrate surfaceand perpendicular to the electrode length dimension. In someembodiments, as illustrated schematically in FIG. 3, the cross sectionshape of both powered electrodes and dividers may be approximatelyconstant along such length dimension.

In some embodiments, the cross-sectional shape of AC powered electrodesmay generally have a rectangular cross-section with rounded corners asseen in FIGS. 3, 4 a-l, 5, 6, 7, 8, 9, and 10.

Embodiments of the present invention may use PGUs in variousconfigurations and combinations to achieve desired processingcharacteristics. In example embodiments, PGUs may be used for processinglarge substrates or carriers holding smaller substrates, or continuousband substrates. In some embodiments, an elongated PGU or a row or anyarray of elongated PGUs may be used to process a large area substratefor PV panels or other applications. In some embodiments, a linearplasma source or plasma generating unit (PGU) can be configured tooperate effectively with a variety of processes, providing efficient gasutilization for the desired substrate reactions in combination withshort and uniform gas residence time to prevent unwanted gas phasereactions. In some embodiments, multiple PGUs may be used to enhance thethroughput of the overall system and still allow the flexibility to tuneeach unit for specific process steps to suit the requirements of theapplications.

In example embodiments, one or more PGUs may be positioned near thesurface of the substrate to be processed, each supporting one or moregas discharge(s) that generate plasma and reactive species in volumesadjacent to the substrate for processing its surface. If multiple PGUsare used, some or all may be of the same configuration and may begrouped in combination with some of the different configurations invarious kinds of mixtures. A PGU in some embodiments, particularly wheresuch PGU may be used singly or substantially spaced from another, mayinclude as elements two or more electrodes which are either grounded orpowered. In example embodiments, at least one of the electrodes in eachPGU is powered, and in particular may be provided with RF or VHFcurrent. In some embodiments where there may be multiple,closely-grouped PGUs each may have one or more electrode(s) aselement(s), at least one of which is provided with RF or VHF current. Inboth isolated and grouped configurations a PGU may or may not have aselements one or more divider(s), which may not be grounded or powered,but may be electrically floating. In some example embodiments, the PGUsare generally capable of generating plasma between their poweredelectrodes and the substrate, as well as between elements within thePGU, or between an element of the PGU and an element of an adjacent PGU.In some embodiments, the opposite side of the substrate or carrier maybe supported on or very near a neutral electrode that may be grounded orhave a small impedance to ground at RF, or VHF frequencies. In someembodiments there may be plasmas formed between adjacent elements thatmay provide for activation and ionization of gas before or after thesubstrate has been exposed to it.

In example embodiments, the plasma(s) may cause processing to take placein one or more elongated region(s) over the surface of the substrate(s).In some embodiments, each of the processing regions formed by a PGU islarger in one dimension than the diameter or width of the substrates ormay be comparable in size to a large dimension of a carrier (forexample, the outer width of the carrier). In example embodiments, theprocessing regions formed by the PGUs over the substrate surface may beelongated and the length of each such region may be much greater thanits width. For example, the length of each processing region between aPGU and the surface of the substrate may be between two and 100 timesthe width of the processing region in example embodiments or any rangesubsumed therein. If there are multiple PGUs in a chamber in someembodiments, the PGUs may be arranged closely spaced side by side sotheir elements have long dimensions aligned and are approximatelyparallel to each other with gaps comparable in magnitude to those gapsbetween elements within a PGU or between electrodes and the substrate,or they may be spaced apart from each other or separated from each otherby other by spacers or dividers (which, in some examples, may be purgedwith inert gas).

In some embodiments the PGUs may be placed in close proximity to eachother without need for a shield between them. This configuration may beused to provide a stable means of running multiple units next to eachother which may be performing different process steps. If necessary fora particular application, the specific process performed by each PGU maybe independently adjusted by incorporating features, such as differentelectrode and divider configurations in a PGU, individual gas flowcontrol for varying the gas mixture, separate power supply connection,different liner configurations, electrode width and height, electrodegap distances, length of pre-activation region above the process gasinjection point, and/or size of the process region.

In example embodiments, elements within PGUs may be generallyproportioned and shaped to process substrates uniformly. The lengths ofelectrodes or divider(s) within a PGU may be greater than the dimensionof the substrate(s) aligned along such length, and lengths may be muchgreater than either their height—the size in the direction perpendicularto the substrate—or their width or both. The width dimension of anelectrode or divider is defined as its size parallel to the substratesurface and perpendicular to its long dimension. In some examples, thelength of the electrodes may be two, ten, twenty, fifty, one hundred ormore times the height or width of the electrodes or both. Examplelengths of electrodes, dividers or other elements in the PGU may be fromabout 30 centimeters to about 400 centimeters or any range subsumedtherein. Example heights of electrodes, dividers or other elements in aPGU may range from about a centimeter to about 30 centimeters or anyrange subsumed therein. Example widths of powered electrodes, dividersor other elements in a PGU may range from about one centimeter to about30 centimeters or any range subsumed therein. The ratio of poweredelectrode height or width to length may be less than about 0.25 in someembodiments. The heights of grounded electrodes or dividers may bewithin the same range as those of powered electrodes in exampleembodiments. However, the minimum widths of grounded electrodes ordividers may be less than for powered electrodes and may be as small asabout a millimeter in some embodiments. Example ranges for the width ofgrounded electrode and divider may be between about 1 millimeter andabout 100 millimeters or any range subsumed therein, with widths withinthe range of between about 2 millimeters and about 10 millimeters beingused in some example embodiments.

In embodiments where the substrates move relative to the PGU duringprocessing the substrate may move roughly in the direction of the widthdimension of the elements and roughly perpendicular to the elements'length dimension. Example electrodes may be made at least partially ofelectrically conducting material such as metal, although they may alsohave parts which are poorly conducting. Electrodes cross sectional shapeperpendicular to their length dimension may be generally rectangular insome embodiments but variations in such shape may be appropriate forsome applications. Electrodes may either be connected to a source of RF,VHF, UHF or microwave current or energy, or may be connected to groundthrough reactive or resistive circuit components whose impedance is notexcessively large. Dividers are in some embodiments approximatelyparallel to electrodes along their length dimension and may be ofinsulating or conducting material or both. If made all or partially ofmetal, that part of a divider may float electrically and be neithergrounded nor be connected to a power source. In general, dividers mayserve as conduits for gas flow and may also serve as a boundary for aregion within which plasma is sustained. In some examples, electrodesand dividers may be supported either by a support structure on theirside facing away from the substrate which may include dielectric andpossibly metal, or at their ends in the direction of elongation.

In example embodiments, the elements of a PGU may be closely spaced fromthe substrate surface to be processed and from each other. An electrodewithin a PGU may have the same or different width from another electrodeor divider, and its minimum distance from the substrate may be less thanor approximately equal to either its width or its height, or both. Insome embodiments such distance is much less than either the width orheight. Such distance to the substrate may be approximately constantalong all or most of the lengths of the electrodes and dividers.However, in some embodiments, such distance may vary, especially nearthe ends of electrodes, in order to counteract other end-effects in theplasma so that the process variation at the ends has reduced variationand acceptable uniformity over a greater fraction of the PGU length.Elements within a PGU, including both electrodes, and dividers, if used,may be closely spaced to the adjacent element(s) along the substantialpart of their lengths. In some embodiments, some facing surfaces may beangled slightly in a plane perpendicular to the length dimension and maybe substantially parallel along most of such length.

In example embodiments, the substrate is supported either on a neutralelectrode directly or on a carrier that is supported on it. Thesubstrate may be placed directly on the support, on intervening spacers(conducting or insulating), or suspended by the differential pressure ofa gas cushion. In example embodiments, when a configuration with astationary PGU and moving substrate is used, the parts that accomplishthe substrate motion may either fully or partly form the neutralelectrode, or act as non-conductive separation between the substrate andneutral electrode. In some embodiments, the neutral electrode may begenerally more extensive along the direction of substrate motion thanthe powered electrodes so that there may be a common neutral electrodefor multiple PGUs containing powered electrodes.

During substrate processing in some embodiments, gas is injected andflows toward the substrate within an element or between two elements,which may include electrode(s) or divider(s) or both. In someembodiments, such element or elements may be a powered electrode and anadjacent element or two dividers. In some embodiments, the plasma thendiverts and flows parallel to the substrate surface, eventually flowingbetween a powered electrode and the substrate, and then diverts to flowbetween that electrode and a neighboring element and then to an exhaustport from the processing chamber. Such diversion in gas bulk flowdirection may in some embodiments be by about 90 degrees. Such diversionin gas flow direction occurs in example embodiments without causing arecirculating flow pattern of the gas.

In some embodiments, the electrodes may have some edges rounded orbeveled, in particular for one or more of the edges bounding that sidefacing the substrate, so that said diversion of the gas flow occurswithout causing recirculation flows within the volume downstream fromthat edge. Further, it is also helpful for avoiding recirculation flowsthat the gap between such elements with rounded or beveled edge(s) andthe facing surface, toward which the gas is flowing, be small so thatrecirculation flows are avoided. In some embodiments, such gap should beless than about three times the width of the channel which is diverting.Such careful control of the flow pattern of the gas may be important foroptimum process performance in some applications, such as deposition ofnanocrystalline silicon for thin film silicon photovoltaic panels. Suchrounding or beveling of otherwise sharp edges may also be advantageousfor either conducting or dielectric film deposition. In exampleembodiments, the gap between powered electrodes and substrate may be inthe range of about 5 mm to 15 millimeters or any range subsumed therein.Based on this, and example pressure and gas flow ranges, the rounding ofthe edges appropriate to avoid recirculation flow may be in the range ofabout 1 mm to 10 mm in example embodiments or any range subsumedtherein.

While gas may be ionized in the spaces between powered electrode(s) andthe substrate in example embodiments, plasmas may also be formed inspaces between powered electrode and an adjacent element or betweennearby elements in some embodiments, wherein gas may be flowing eithertoward or away from the substrate. In some embodiments gas may beactivated by plasma during its initial flow toward the substrate. Suchgas may include an inert gas and/or a gas/gases that chemicallyparticipate in the process, which may include either atomic or molecularspecies. If such gas is activated during passage between elements of aPGU, it can facilitate the breakdown or dissociation of the feed gasthat provides the reactive species for substrate treatment. In someembodiments injected gas may flow toward the substrate in the spaceadjacent a powered electrode or in the space between divider andelectrode or between two dividers or two electrodes. Whether or notactivated, such gas may in some embodiments provide chemical isolationbetween adjoining processing regions associated with neighboring PGUs.Helium is one such gas that may be used to provide isolation withoutsubstantial chemical effects on other gases. In some embodiments wherethe gas injected toward the substrate can be more easily activated byelectron impact than helium, when such gas then flows in the spacebetween an electrode and the substrate it will also participate in theplasma reactions producing various species, some of which may be neededfor the process.

For optimized process conditions in example embodiments, the plasmasbetween powered electrode(s) and substrate may have different powerdensity, electron density and electron average energy than regionsbetween electrodes and adjacent elements, depending on the particularapplication. This ability to independently and controllably vary thepower densities in such adjacent plasma regions is a consequence of theelectrode structure as well as the close control of the relative sizesof gaps between powered electrode(s) and substrate versus gaps betweenelectrode and adjacent elements. The phase between the time-varyingelectrical potentials fed to each electrode in a PGU can also be variedto tune the relative power density in the gap between the poweredelectrodes versus the power density in the process region between thepowered electrodes and the substrate. In some embodiments, such ratio ofgaps can be varied by up to about 50% for the various applications. Insome embodiments, the plasma between electrode and substrate willreceive a higher power density from the electrode, and be of higherelectron density and average energy than plasmas between electrode andadjacent elements. This will be particularly appropriate when eithergeneration of reactive radicals immediately adjacent the substrate, orion bombardment of the substrate are limiting or controlling reactionsfor that process application. On the other hand, in some embodiments ofthe process, such as deposition of silicon nitride with very lowhydrogen content, the formation of nitrogen atoms by pre-dissociation ofN₂ gas requires a great deal of energy and benefits from a configurationin which the plasma between a powered electrode and the adjacent elementis of higher power density than that between the electrode and thesubstrate.

For processes requiring ion bombardment as a primary mechanism—such asreactive ion etching—the power density to the plasma, D_(p), which isgenerally expressed in units of Watts per cubic centimeter perkiloPascal of pressure, will be higher than for processes where neutralspecies only are required, such as deposition of nanocrystallinesilicon. Typically, ion-based processes will be characterized by a rangeof power densities that is roughly between about 3 and 100 W/cm³/kPascalor any range subsumed therein, whereas neutral-based processes may haveD_(p) between about 0.1 and about 10 W/cm³/kPascal or any range subsumedtherein.

Such low power densities may be used for plasma-assisted depositionprocesses to avoid ion damage to the deposited films so that defectlevels can be at or below a level that permit, for example, highphotovoltaic efficiency in deposited silicon. In the case ofnanocrystalline silicon, the defect levels may be less than or aboutseveral times 1016 per centimeter cubed. To achieve a high stabilizedphotovoltaic efficiency, above about 13%, it may be desirable to limitsuch defect levels below about 2×10¹⁶/cm³.

Shapes and positions of dividers, and electrodes may in some embodimentsbe chosen to greatly improve chemical isolation between adjacent PGUswhen inert gas is injected through or between them. In some embodiments,the gap between the divider and the substrate may be very small,potentially as small as 0.05 mm or even less, to improve such isolation.In some embodiments the separation of a grounded electrode from thesubstrate may be very small. In some embodiments a substantial flow ofinert gas such as helium or argon is injected through a groundedelectrode or divider into a very narrow gap between itself and thesubstrate. In this case the gas may not be pre-activated by suchpassage. Such gas may also be injected between two closely spacedelements such as two dividers or grounded electrode and divider orpowered electrode and divider so as to minimize diffusion of a processgas or gases from one PGU into the adjacent PGU where a differentprocess step may be performed. This can be used to cause the flow of theprocess—causing species to consistently be in the same direction—whichmay be important if the substrate is moving relative to the PGU. In thiscase, whether or not there are multiple PGUs the direction of reactivespecies flow can be chosen to be either along or in the directionopposite to that of the substrate relative motion.

In some embodiments where there is a very small gap between divider orgrounded electrode and substrate, and inert gas is injected through thedivider, this can act as a sort of “gas bearing”. Use of sufficientflows of gas and shaping of the divider(s) and possibly electrode linermay help prevent contact of the substrate with this element and helpmaintain more precisely the position of the substrate relative to theelectrodes whether the substrate is stationary or moving, but especiallywhen the substrate is moving. This may be important in controlling theprocess and making it have less variation in time due to fluctuations inthe gap between powered electrode(s) and substrate. It is further usefulin some embodiments that there be both injection of gas through adivider or between dividers as well as pumping through a differentdivider or between a different pair of dividers adjacent the location ofinjection, so that there can be a true gas bearing which maintains avery nearly constant gap between the dividers and the substrate. Thismay help maintain a constant gap between powered electrodes andsubstrate and therefore controlling and/or making constant in time theprocessing rate, which may depend on such gap. In this case the ratio ofthe power densities in the plasmas between electrodes or electrode anddivider relative to the power density between electrode and substrateare kept more constant and may provide for better consistency in processresults.

In general as gas flows through a series of channels it may undergoexpansion and its bulk flow speed will decrease if the cross sectionalarea of the channel through which it flows increases. Such flow into anexpanded channel or region may cause gas cooling. In exampleembodiments, a flow channel may to have an area with width equal thelength of the electrode or divider, and height equal the distancebetween the bounding electrode, substrate or divider surfaces. Contraryto the case of an expanding channel, the gas will tend to accelerate andundergo some compression if the cross section area of its flow channeldecreases. If the walls of the channel get hotter or the gas is heatedby plasma the flow speed will tend to increase, while cooling walls willcause deceleration. In example embodiments, there may be a change in thecross sectional area of the channel along the flow path of the gas, andin plasma power density and/or the wall temperatures such that the gastemperature and/or bulk flow speed will change as it moves from oneplasma region to another. In particular, the temperature of the gas maydecrease slightly as it flows from the region between powered electrodeand substrate into the region between elements on its way to the exhaustdue to lower power density in the plasma in this region. However, inexample embodiments, any such decrease in gas temperature may be smallso that particulate growth in this region is minimal and does notadversely affect the results of the process. In example embodiments,such “effective” cross sectional area of the flow channel does notchange by more than about a factor of three, and the power density inthe plasma does not decrease by a large factor (for example, more than10 times) from one region to the next, so that abrupt cooling of the gasstream is avoided. In some processes said abrupt cooling would result inrapid growth of particulates in the gas phase which would causecontamination on the substrate and poor process performance. In somecases the “effective” flow channel cross section area for a particularflow path may be less than the full channel area when gas flows from asingle channel into two separate channels. Conversely, when flowcombines from two initial channels into a single channel the effectivechannel cross section of the flowing gas from each initial channel inthe combined channel may effectively be less than the full area of thecombined channel as regards its effect on gas expansion and cooling.Further, by keeping plasma power density and/or wall temperatureselevated along most or the entire flow path the gas may be kept hotteralong the entire flow path so that the gas temperature does not changemuch during its passage through the reactor. This, along with avoidingof large increases in the cross sectional flow area prevents sudden gascooling or slowing in bulk flow speed during its residence time in thereactor, may result in reduced particle formation in some embodimentswhere depositing species are present in the gas phase, which for someapplications may improve process performance. Since particle growth isso much faster in gases where the temperature is less than about 100°C., the gas temperature may be kept above about 100° C. throughout theflow path of the plasma in example embodiments. Example embodiments maymaintain such high gas temperature because it avoids rapid expansions inthe cross section for flow and maintains all surfaces in contact withthe gas flowing through the plasma above about 100° C.

To enhance the ability to control plasma activity in the exhaustmanifold in example embodiments, additional electrode(s) may be added aspart of the exhaust manifold relative to the previously describedconfigurations. A gas that improves the volatility of gaseous reactionbyproducts, and/or volatilizes deposited films may also be added to theexhaust region during the deposition cycle. This cleaning gas may, ormay not need to be activated by plasma activity.

After a certain amount of continuous processing, a complete cleaningcycle may still be required in some embodiments. A complete cleaningcycle may involve injecting a cleaning gas via the input manifolds thatvolatilizes films and particles deposited on the liner or electrodesurfaces. The reaction of the cleaning gas may be activated by plasma,temperature, or both. The cleaning cycle may be performed on the heatedliners directly after a deposition cycle, or the liners may first beheated by an additional heating mechanism for cleaning, such as a plasmacreated by a non-reactive gas.

A particular issue pertaining to in-situ cleaning of processing systemsis that the amount of contamination to be cleaned may not be uniformlydistributed. For example, in silicon deposition systems the exhaustregion may need more cleaning than the processing region, which in turnmay require more cleaning than the pre-activation region. In addition,the cleaning gas may also attack clean surfaces, creating undesireddamage and particles. In example embodiments, the voltage phases to theelectrodes may be adjusted during the cleaning cycle to be differentfrom the deposition cycle. This method provides the capability toincrease power dissipation to particular regions around each electrodeas required during the cleaning cycle to enhance removal of deposits andparticles where most needed and reduce attack on surfaces that need lesscleaning. Gas composition and/or injection location may also be adjustedduring the cleaning cycle to improve its effectiveness.

In some embodiments the gas injected through an electrode into theprocess plasma may come from two or more separate upper reservoirswithin that electrode that are both connected with a lower reservoirwithin the electrode. The lower reservoir may feed three or more rows ofholes conveying gas into the space between that electrode and thesubstrate. In some embodiments, provision of different gas compositionsto the separate upper reservoirs within the electrode(s) can cause theprocess gas injected from successive rows of injection holes to have acomposition that varies with a desired functional dependence on theposition in the process plasma. This may be used to control the gasphase concentrations of species produced in the plasma to give either adesired uniform process along the width direction, perpendicular to thelong direction of the PGUs, or perform a process with a desirednon-uniformity. In the case of deposition of nanocrystalline silicon,the injection of a gas mixture to the plasma between powered electrodeand substrate having increasing fractional silane or disilane contentalong the direction of bulk gas flow may permit much more uniformproperties of the deposited nc-Si:H film—increasing the photo conversionefficiency of the cells and the value of the process.

In example embodiments, the cross-section of a powered electrode may berectangular with a roughly uniform gap formed between adjacentelectrodes, but more complex shapes and gaps may also be formed ifbeneficial for some applications. Long edges of electrode or dividersmay be rounded with curvature radius chosen to avoid recirculation flowsas the gas stream passes such edges and flow proceeds into the nextregion on its way to the exhaust. The minimum gaps formed betweenpowered electrodes, between powered electrodes and substrate, andbetween electrodes and dividers may all be less than the width or lessthan the height of the electrodes or less than both. Such gaps may varydepending on the position between two facing surfaces, but the amount ofsuch variation may be less than the minimum gap in example embodiments.In some embodiments, the gap is mostly uniform and the facing surfacesare substantially parallel over most of such areas. Said uniform spacingbetween facing surfaces wherein plasma is generated may tend to make theplasma density within such volume more uniform, which may improve theprocess performance. In some embodiments, at least one of the poweredelectrodes in a PGU may also be wider than the gap formed between thesubstrate and powered electrode. This causes the plasma properties insuch region adjacent the substrate to be controlled independently fromthose in adjoining regions and maintains substantial sheath potentialsthat provide particle bombardment to the surface whose energy depends onthe gas density.

The powered electrode(s) may in some embodiments be mounted directly to,or close to, a dielectric structure that may provide conduits for gassupply, cooling water, and gas exhaust, and in some embodiments providephysical support. Inert and/or reactive gases may in some embodiments beinjected from the dielectric structure into the gap region formedbetween two powered electrodes. Gas injection manifolds formed insideone, or both, of the powered electrodes may also be used to supply gasdirectly to the electrode gap and/or processing region. In someembodiments, after flowing by the processing region, gas flows towardexhaust ports near one, or both, of the powered electrodes in each PGU.In some embodiments, the powered electrodes may be connected toappropriate sources of RF, VHF, UHF or microwave current so as to createsustained plasma in such regions where gas is flowing toward theexhausts.

In some embodiments a metal electrode which is connected to a powersource or to ground has plasma-facing surface(s) that are covered bydielectric or weakly-conducting liners. In example embodiments, theseliners may be directly deposited onto the electrodes or may be aseparate body attached to the electrodes maintaining a finite but smallgap to the electrode to allow their surfaces that are in contact withthe plasma to be at a somewhat higher temperature than the electrode. Insome applications it is advantageous that the surfaces contacting theplasma be as hot as possible so that it may be advantageous to usematerials for liners such as quartz or even “opaque” quartz which havelower thermal conductivity in order that the surface temperature behigher for a given heat flux to the surface. Materials may be used, suchas quartz or other dielectric or low-conductivity metal that have a verylow coefficient of thermal expansion so that the liner does not expandvery much relative to the electrode which may be cooled by fluid flow orother methods. The small thermal expansion reduces potential rubbingbetween the liner and inner body and maintains alignment of holes in theliner with holes in the inner body of the electrode—in particular holesthat may be for injecting process gas into the plasma. In exampleembodiments the gap of the inner body to the liner may be less than aminimum distance within which plasma can be sustained at the processpressure, so that there is no plasma generated between electrode surfaceand the liner. The gap between liner and electrode may be chosen basedon the gas pressure and heat flux to the liner so that the temperatureof the liner's outer surface may be profiled in accordance with therequirements of the process. In using such liner(s), the surface of theliner may be the effective interface with the plasma and may be theeffective surface for RF, VHF or UHF currents transmission to the plasmawhether said liners are of conductive or dielectric material. In exampleembodiments, the gap between the electrode and liner may be betweenabout 0.05 mm and about 3 mm or any range subsumed therein, depending onthe gas pressure and AC power density and frequency. Generally, higherpressures and lower AC frequencies make smaller gaps necessary.

In some embodiments, the gap between inner surface of the liner and theelectrode surface, as shown in FIG. 7, is constant within about 10% overa majority of that face opposite the substrate or facing anotherelectrode. In some embodiments, the thickness of the liner isapproximately constant over the majority of the liner area. Inembodiments where both gap and thickness are constant, the AC impedanceof the gap and liner combined in series may be roughly constant overmost of that face of the electrode surface. In this case, when theelectrode surface AC potential is constant and the plasma impedanceapproximately constant over the area of that face, the resulting surfacepotential on the liner will also be roughly constant. Further, in someof the above embodiments, the surface of the liner facing the plasmawill be parallel to the surface of the underlying electrode over amajority of the electrode surface so that the gap from substrate toliner surface will be uniform if the gap from substrate to electrode isuniform.

In some example embodiments, some parts of the liner may be thicker orhave raised ridges or pads with small dimension or dimensions so that inthese places the shield actually contacts the electrode. This may bedone to provide physical support for the shield or liner, to act asbarriers minimizing gas flow between areas in the space between linerand electrode, or to control and keep more constant the gap betweenelectrode and liner over most of its area. In such cases where adimension of such area is narrow or small the effect on the uniformityof the AC impedance of the shield is minimal, preserving the uniformityof the electrical potential of the liner on its outer surface givenuniform surface potential on the electrode. In some example embodiments,there may be narrow grooves or other small shaped recesses in theelectrode surface into which raised or thicker areas of the liner mayfit, but such may not cause substantial potential variation on the outersurface of the liner or perturb the general uniformity of the impedanceof the liner.

In some embodiments, the liner may be designed so that the gap betweenelectrode and liner is controllable and does not vary substantially overtime in different regions of the electrode. In some embodiments, thisgap does not vary by more than about 10% or 0.1 mm, whichever is larger.In some configurations, the space between powered electrodes may bepartially filled by such dielectric liners, but the configuration of gasflows in different plasma regions is not affected. In some exampleembodiments, the size of the gap between liner and inner body of theelectrode(s) may be made to vary with position on the inner body surfacein order to cause the RF, VHF, UHF, or microwave intensity at the outersurface of said liner to have a desired dependence on position. This maypermit the power density injected into the plasma to be shaped asdesired to meet requirements of the process. The thickness of the lineras well as the gap may in some embodiments vary with position so thatthe combined effect of their series impedances causes the power densityof the injected RF, VHF, UHF, or microwave power to have the desireddependence on position. In some embodiments there may be multiple layersof such liners covering such inner body where the gaps between them areso small that plasmas are not formed between any adjacent innersurfaces. While such liners may represent substantial RF, VHF, UHF, ormicrowave reactive impedance, they may also have small enough thicknessand gap that such reactive impedance is not excessive. In someapplications at higher gas pressures (above about 200 Pascals forexample), the gap may be less than about 1 mm in some embodiments.

In some embodiments, the gap causes the liner to maintain a temperaturesubstantially above that in the electrode inner body. Use of differentgas compositions and different gas pressures will in general affect thethermal conduction from the liner to the inner body. Should the mixtureuse substantial amounts of light gases such as hydrogen or helium thetemperature of the liner will be closer to that of the inner body,whereas use of argon as principal gas with minimal amounts of hydrogenand little or no helium will result in higher temperature differentialbetween liner and inner body—which for normal heat fluxes to the linerbetween about 1 and 3 W/cm², the liner may be between about 50° C. and150° C. hotter than the electrode inner body. Walls in contact with theplasma can thus be kept above about 100° C. In this case the gastemperature in the plasma will for modest levels of plasma power beeverywhere hotter than the lowest temperature body in contact withit—typically the walls—and therefore can be maintained above 100° C. orhigher. Gas temperatures throughout the plasma volume may with suchliners be maintained with a minimum between about 100° C. and 200° C. orabove, which may for some applications have beneficial effects.

In order to avoid direct plasma exposure of bare electrode surfaces thatmay have much higher surface voltages and potentially cause variousproblems, a liner configuration may be used that avoids line-of-sightexposure of electrode to plasma. Yet, for some applications gas may needto be injected from the electrode into the plasma via a providedconduction path. Some embodiments of such a liner may include bafflescovering any hole or narrow slot in such liners, where such baffles arespaced narrowly from the rest of the liner on three sides so that thegas flows around the baffle and then through holes or slots into theplasma. If gaps are narrow no plasma will be sustained therein and veryfew ions will strike the electrodes.

In some embodiments, there are two opposite directions of gas flowacross the substrate, both perpendicular to the long direction ofelectrodes and parallel to the substrate surface, while in otherembodiments there may be but a single direction of bulk flow of gasalong the surface of the substrate. Single direction flow can in someembodiments be accomplished by use of dividers which have very smallgaps to the substrate, and where inert gas may be injected so as togreatly reduce flow of process gas in the direction from the region ofprocess gas injection toward said inert gas injection. In someembodiments the substrate moves relative to the PGU. In this case theflow of gases may be either bi-directional with flow in some areas alongthe direction of apparent substrate motion and in other areas oppositeto it. In other embodiments the flow may be only along the direction ofthe substrate's apparent motion as observed from the PGU, oralternatively may in some embodiments be opposite to the substrateapparent motion.

In some embodiments, the space between two powered electrodes in a PGUmay be completely filled with an insulating material and all gases maybe introduced through holes in the powered electrodes. The electrodeslower surfaces that face the depositing plasma may also be covered byone or more insulating liners. The outermost such layer may have smallholes that support hollow cathode discharges that can cause utilizationrate of the feed gases to be higher than in normal parallel platedischarges.

Additional examples of PGU configurations which may be used in exampleembodiments are schematically illustrated in FIGS. 4 a to 4 l. ThesePGUs, for example, may be used as the PGUs in processing chambers 100 or200 or may be used in other configurations as described above.

FIG. 4 a illustrates an example embodiment with a PGU having twoelectrodes, 401 and 402, wherein gas flows toward the substrate betweensaid electrodes, both of which may be provided alternating current froma power source which may be at RF, VHF, UHF or microwave frequencies, orcombinations thereof. The gas stream flows to the substrate, 400, andsplits, diverting so some gas enters the region between each electrodeand the substrate, and then after flowing past such electrodes divertsagain to flow upward between each electrode and the adjacent surfaces,or elements on both sides which may be elements of another PGU, orend-pieces wherein plasmas may in some embodiments also be formed. Itshould be noted in FIG. 4 a that gas flow direction, after issuing fromthe gap between powered electrodes, is to the left under the poweredelectrode 401 and to the right under the electrode 402. The result isthat gas flows in opposite directions through the adjacent two regionsof the substrate that face the two electrodes. As shown in FIG. 4 a, theelectrode surfaces facing the substrate are mostly flat in the depictedembodiments and parallel so that the gap within which the gas flows isnearly constant, creating a nearly constant cross sectional area of thechannel through which the gas flows. The gaps between poweredelectrodes, between powered electrodes and substrate, and betweenpowered electrodes and outside structures may all be set independently.In some embodiments, such different gaps should not have sizes so muchdifferent that the gas experiences substantial expansion along its flowpath. Thus, gas is, from the point of injection, flowing successivelythrough volumes whose cross sectional area does not increase by a factormore than about two. Thus, even as the gas diverts in its flow pathwithin the chamber it does not undergo significant expansion or cooling.

In some embodiments having two powered electrodes, such as in FIG. 4 a,such electrode surfaces facing either the other electrode or thesubstrate need not be flat or parallel so that slight gas expansion andcompression does occur during flow in each region. Yet, some embodimentsmay limit such volumetric expansion or compression along the flow pathto less than a factor of about 2 so that gas cooling in such locationsis not excessive.

FIG. 4 b illustrates an example configuration of a two electrode PGUwherein one is grounded, 411, and the other, 412, is providedalternating current which may be at RF, VHF, UHF or microwavefrequencies or combinations thereof. Said grounded electrode 411, may ormay not have an insulator segment at its end adjacent the substrate. Insome embodiments the gap between the substrate, 400, and the bottom ofthe grounded electrode 411 is small compared to the gap between thesubstrate 400 and bottom of powered electrode 412 to induce the gasinjected from the top between the grounded electrode 411 and the poweredelectrode 412, which may be inert gas, to flow substantially to theright under the powered electrode 412 due to the effective barrier togas flow provided by the narrower gap to the substrate at the bottom ofthe grounded electrode. In order to make this barrier effective, the gapbetween such grounded electrode, 411, and the substrate, 400, may insome embodiments be very small much smaller than that between thepowered electrode and the substrate so that little or no plasma isgenerated in this gap. In some embodiments gas for the process may beinjected from the bottom of the powered electrode, 412, into the regionbetween that electrode and the substrate. In some embodiments inert gasmay also be injected through the grounded electrode into the gap betweenit and the substrate. In embodiments where inert gas is injected fromthe bottom of the grounded electrode, that gas may flow in bothdirections, to left and/or right, so that gases flowing on either sideof the grounded electrode are largely kept separate. The formation offlow barrier may be most effective when the gap between the substrateand the grounded electrode is less than about 2 mm, and in someembodiments less than or about 0.2 mm but more than about 0.02 mm. Theeffect of such a small gap is illustrated in FIG. 4 b, minimizing theflow of process gases toward the left from the region under the poweredelectrode and more effectively makes the direction of flow of processspecies in the PGU only to the right. The resultant pattern of flow ofgas sequentially being first down flow towards the substrate betweengrounded and powered electrode, then diverting such flow to pass betweenpowered electrode and substrate, and then diverting again, inembodiments having multiple adjacent such PGUs, into an up flow awayfrom the substrate between the powered electrode and the groundedelectrode of an adjacent PGU. Such flow pattern may be continued inadjacent PGUs and other PGUs of the same design present in the chamber.In this way, in embodiments where there is a substrate moving to theright or left relative to the PGU, the flow of process gases may be madeunidirectional either along the direction of the substrates motionrelative to the PGU, or opposite to that motion. Such unidirectional gasglow could, for some applications, be useful in improving processresults relative to those having bidirectional flow such as in FIG. 4 a.In some embodiments such flow may be in the same direction as themovement of the substrate relative to the PGU.

In some embodiments exemplified by FIG. 4 b the injection of inert gasthrough the bottom of the grounded electrode 411 can prevent thesubstrate moving up to touch the bottom of the electrode and helpcontrol the gap between the grounded electrode and the substrate.

FIG. 4 c schematically illustrates an example embodiment of a PGUconfiguration similar to that of FIG. 4 a, but which may be used whenadjacent PGUs are performing processes using different gas mixtures, andthere is need for processes gases in adjacent PGUs to be isolated. Inthis case, in addition to the powered electrodes, 421 and 422, there isa grounded electrode, 423, with a very small gap to the substrate,similar to that in FIG. 4 b, which also may serve for injecting inertgas both adjacent to it and through it. In some embodiments the flowpath of the gases starts between the powered electrodes wherein gasinjected from the top moves toward the substrate, 400, and then afterpassing the electrodes the flow divides into two paths in to the regionsbetween each of the two powered electrodes and the substrate. Afterpassing through the regions between the powered electrodes and thesubstrate the flows in both directions divert again and move upward awayfrom the substrate and then to the exhaust. This path for upward flow isformed for electrode 422 by the gap to the grounded electrode 423. Forpowered electrode 421 the upward flow path is formed either by the gapto an adjacent PGU, or an element that is part of the chamber 100 or200. In the embodiments illustrated by FIG. 4 c there may be gasinjection from each powered electrode into the gas and plasma regionbetween itself and the substrate. In some embodiments there may also beinjection of process gases from one or both powered electrodes into thespace between the two powered electrodes, 421 and 422. Also, there maybe liners covering the powered electrodes and there may also be a linercovering any grounded electrode in each such PGU. The AC power providedto the electrodes may be from the RF, VHF, UHF or microwave frequency,or combination thereof. In some embodiments there is plasma in the spacebetween powered electrodes, between powered electrodes and the substrateand between powered electrodes and grounded electrodes. In someembodiments the power densities and electron densities of any suchplasma does not differ from any other by more than about a factor of 5.In some embodiments the edges, 404 in FIGS. 4 a and 424 in FIG. 4 c, ofthe side of the powered electrodes facing the substrate may be roundedwith curvature radius such that the gas flows continuously from oneregion to the next with a laminar flow and without recirculation.

FIG. 4 d schematically illustrates an example embodiment of a PGUconfiguration having a powered electrode and a divider that is notelectrically grounded. The divider 431 does not establish a strongelectric field between itself and the powered electrode 432 and can,therefore, be placed in close proximity to the powered electrode. Thedivider can, for example, be made from dielectric material or of aconducting material if it is not connected to any ground or powersupply. Gas is injected between the divider, 431, and powered electrode,432, which then flows down toward the substrate, 400. The gap betweendivider and substrate may be smaller than that between powered electrodeand substrate so that the gas injected between divider and electrodealmost entirely flows to the right and under the electrode. Further,process gas may be introduced from the powered electrode into the regionbetween itself and the substrate. Thus, the gas stream which initiallyflows downward diverts to flow under the electrode and then havingpassed the electrode diverts to flow upward away from the substrate. Thegap between divider and electrode in some embodiments may be small sothat the gas flowing through it does not break down and becomeactivated. Alternatively, in other embodiments the gap may be sufficientfor such gas to break down and be activated. Inert gas may also beintroduced at the bottom of the divider so that it purges the gapbetween it and the substrate and provides a further barrier assuringthat the gases injected from the electrode flow to the right. In someembodiments of this configuration there may be other PGUs closely spacedas in FIG. 1 so that the gas flowing upward will also be broken down toform a plasma between PGUs. Some embodiments have rounded edges on thebottom edges of the electrodes or dividers so that the gas flowingaround them will do so in a non-recirculating manner.

FIG. 4 e schematically illustrates an exemplary embodiment of a PGU witha central element, 442, which may either be a grounded electrode or adivider between two powered electrodes, 441 and 443. The gas injectionpaths toward the substrate in this embodiment are formed by the two gapsof the central element 442 to the two adjacent powered electrodes 441and 443. Gas flowing towards the substrate diverts after exiting the gapformed along the powered electrodes, resulting in flow in oppositedirections along the substrate surface into the regions under each ofthe powered electrodes 441 and 443, and the substrate 400. After passingunder the electrodes 441 and 443 the gases divert to flow away from thesubstrate in the gaps formed between the electrodes and elements ofadjacent PGUs on either side, or other adjacent structure or wall partof the chamber 100 or 200. The divergence of the injected gas flow canbe enhanced by making the gap between the central element 442 and thesubstrate 400 smaller than the gap to the substrate between the twopowered electrodes 441 and 443. FIG. 4 e also illustrates an optionalfeature of gas injection from the bottom of the central element into thegap between it and the substrate 400. The addition of injection at thebottom of the central element serves to further isolate the chemicallyactive species from one side relative to the other and to reduce gasrecirculation in this region. Such a configuration is most appropriatewhen one or a few PGUs are used in a chamber, and deposition of morethan one type of layer is required and, in particular, when the gaseousspecies necessary for formation of one layer is a contaminant for theformation of adjoining layer. In this case the isolation of the gasesfor one PGU process from an adjacent PGU process is an importantadvantage of this embodiment. In other cases the reason might be thatthe duration of the process or thickness of deposited layer should bevery small and precisely controlled.

When a similar application as discussed in relation to FIG. 4 e is to beperformed, but a central exhaust is desired, then the configurationillustrated schematically by FIG. 4 f may be suitable. This embodimentmay use the same configuration as in FIG. 4 e with a central element,452, which is a divider or grounded electrode, and powered electrodes,451 and 453, on either side. It can be seen that the principal visibledifference between FIGS. 4 e and 4 f is that the gas flow direction isreversed so that gases are injected on the right and left sides of thePGU and exhausted adjacent the central element. If 452 is a groundedelectrode then AC power to the two electrodes act independently, and thepower feed to the two may be equal or different. In the case where thecentral element is a divider, if plasma is desired in the centralchannels on either side of the central element, the AC power to the twoelectrodes should be different—either out of phase or of differentfrequencies. As described previously in other embodiments, gas, whichmay be inert, may be injected from the base of the central element toimprove the chemical isolation between the two sides.

FIG. 4 g schematically illustrates an embodiment of a PGU with aunidirectional flow adjacent the substrate and chemical isolation fromone PGU to the adjacent PGU. In this case, gas for activation orprocessing may be injected toward the substrate from between poweredelectrodes, 461 and 462, as well as between the left-most electrode andthe adjacent PGU or structure. Gas may also be injected from the base ofeither or both powered electrodes. Further, the element on the right,463, may be either a divider or grounded electrode, which also may serveas a source of inert gas or process gas. This configuration may be mostappropriate when a process for surface treatment, etching or depositionin a PGU requires sequential or blended chemistries, or the process inthis PGU should be isolated from that in an adjacent PGU, or region.

FIG. 4 h schematically illustrates an example embodiment of a PGU thatcan accomplish chemical isolation between different PGUs or groups ofPGUs. In this embodiment, two passive elements, 471 and 472, which areeither grounded electrodes or dividers or one of each, serve to conductgas through a narrow gap or channels between them to the spaceimmediately adjacent the substrate. Such gap may be as in previousfigures between about 0.02 mm and about 2 mm. The two passive elements471 and 472 may have different gap distances to the substrate—within theabove stated range—so as to cause the majority of said gas to floweither to the right or left. Such gas may in some embodiments bepreferably inert so as to chemically isolate the regions to the left andright of this pair of elements. When better chemical isolation isdesired between PGU the gaps between such passive elements and thesubstrate may be in the range between about 0.5 mm and 0.02 mm. To theright of said pair of passive elements is an AC powered electrode, 473.Such power may sustain plasma between electrode 473 and the element 472which may activate gas injected down between these two. The flow patternof gas in the PGU may be similar to that in FIG. 4 d where process gasesmay be injected from the bottom of the powered electrode mixing with thegas flows previously described. This configuration is relatively easilyfabricated, and in some embodiments the two passive elements may be heldtogether with the gap between them being so narrow that plasma may notbe sustained within. In this case the gas is not activated, and mayserve only to purge that very narrow gap between such passive elementsand the substrate, 400.

In case pre-activation of gas is not required before gas encounters thesubstrate, the configuration of FIG. 4 i may be used instead of thepreviously discussed configuration described by FIG. 4 h in exampleembodiments. In this case the two passive elements, 481 and 482, whichmay be either grounded electrodes or dividers or one each, have a narrowgap both between them and between element 482 and the powered electrode,483. Gas may be injected through the space or channels between thepassive elements and between element 482 and electrode 483. Said gas maybe inert gas and causes a degree of isolation of the gas chemistry tothe left of the passive elements from that under the powered electrode.As said gas stream is passing under the electrode, 483, additional gasmay be injected into it from the bottom of this electrode to adjust thegas mixture in the region between the electrode and substrate 400. Afterpassing through this region the gas flow diverts away from the substrateto the exhaust via the gap formed between the powered electrode 483 andelements from an adjacent PGU, or element or wall part of the chamber100 or 200.

FIG. 4 j schematically illustrates an embodiment of a PGU that can helpaccomplish smooth gas flow or avoid recirculation. In this case adivider, 491, is adjacent and closely spaced from a powered electrode,492. There is also a second divider, 493, on the other side of thepowered electrode and a second powered electrode, 494, furthest to theright. In some embodiments dividers 491 and 493 may be identical or verysimilar and the electrodes 492 and 494 may be of similar shapes. Saidelectrodes, 492 and 494, may have insulating protrusions at theirbottoms as shown, or preferably an enlargement of an insulating linersuch that the gap between this feature and the substrate, 400, is verysmall. When gas is injected between said divider and the electrode itflows out the bottom into a narrow gap adjacent the substrate and mayserve to purge this region and prevent gas mixing between regions at theleft and right sides. Gas may also be injected from the bottom of theelectrode, 492. After passing the electrode the gas diverts to flow awayfrom the substrate between that electrode and the adjacent divider, 493.

FIG. 4 k schematically illustrates an example embodiment of a PGU withan additional divider which may help to minimize or eliminate stagnationflow regions adjacent to the substrate. This embodiment is that of FIG.4 a with an added feature so the numbering is repeated for their commoncomponents. Gas is injected and flows toward the substrate betweenpowered electrodes, 401 and 402, divides upon reaching the divider, 403,and two separate streams then pass in opposite directions under the twopowered electrodes. Additional gas may also be injected from theelectrodes to combine with the flow already passing along the substrate.After the gas streams pass through the regions below each electrode itis diverted away from the substrate surface along the opposite side ofeach electrode by the means previously described in other embodiments. Adivider 403, may be located with a very narrow gap to the substrate,400, so as to suppress plasma in the narrow space between them. Thiskind of divider may also be supported from above as part of a longerdivider structure. In embodiments where the divider, 403, is made ofdielectric material, such as quartz or aluminum oxide, it may have aminimal effect on the plasma discharge sustained by the AC currents tothe powered electrodes. Should the divider be made of metal or othergood conductor it may serve to enhance plasma density in those regionsbetween itself and the two adjacent electrodes.

FIG. 4 l schematically illustrates an example embodiment of a PGU thatcombines the features of a unidirectional flow along the substratesurface and control of the gap distance to the substrate 400. Here, theelement, 495, which may be a divider or grounded electrode, has a shapethat promotes recirculation-free flow of gas injected between itself andthe powered electrode, 496. Gas may be injected from the underside ofthe element, 495, so as to purge the narrow gap between that element andthe substrate, 400. Such purge serves to chemically isolate regions atthe left from regions at the right of said element. The shape of saiddivider is such as to maximize the gas pressure in the gap to furtherpromote chemical isolation. The gas flow from said element may alsoprevent the substrate from touching the bottom of said element, andthereby help control the gap between powered electrode and substrate.Further, in some embodiments there may be a duct also within saidelement that leads to an exhaust so that some of the gas that isinjected from the bottom of this element is also pumped out before itcan flow into the region around the powered electrode. This may help tominimize the effect of such gas participating in the process. Inembodiments including such feature the gap between the element, 495, andthe substrate, 400, may be so narrow that the combined injection andpumping of gas serves as a gas “bearing” which serves to exert gaspressure that keeps the substrate within tighter limits at the desireddistance from the powered electrode. This may be of particularimportance when substrates are moving relative to the PGU and“oscillations” of the substrate may otherwise cause substantialvariation in the gap to the powered electrode resulting innon-uniformity of process characteristics. Thus, such a feature as thedivider both isolates the adjacent regions chemically from each otherand helps keep more stable the gaps from electrodes to substrate. Thesemay be important for improved control uniformity and repeatability ofprocesses performed on the substrate surface.

In some example embodiments, as shown in FIG. 5, two powered electrodesin a PGU, 501 and 502, are connected to source(s) of RF, VHF, UHF ormicrowave power such that the instantaneous electrical current to oneelectrode, 501, is approximately equal in magnitude and opposite in signto that of the other, 502. In the illustrated embodiment the poweredelectrodes are roughly mirror images of each other with a gap into whichprocess gases are injected from a manifold, 503, through small holes,504. In this gap there is also sustained plasma, 505, formed by theelectrical breakdown of the gases due to the AC electrical potentialdifference between electrodes 501 and 502. There is also a supportstructure (which may be a neutral electrode), 506, on the opposite sideof the substrate or carrier for substrates, 507, which is a neutralelectrode, which may be connected to ground via a complex impedance Z,511. This impedance 511 may come simply from a physical gap or strap(s)or from electrical components that are resistive, reactive (such ascapacitors and inductors), and/or solid state elements such as diodes orvaristors. The neutral electrode, 506, may physically support thesubstrate or a carrier for substrates. In this example embodiment, theneutral electrode, 506, is effectively a third electrode for each pairof powered electrodes such that together they comprise a triode. On theside of the electrodes opposite to the substrate, in some embodiments,there may be a dielectric support structure, 508, that serves to supportand position electrodes 501 and 502. In some embodiments the supportstructure may be of metal with electrodes supported through standoffsmade of insulating material. Alternatively, in some embodiments thesupport structure for powered electrodes may be the chamber wall and/orvacuum wall with standoffs made of insulating material.

The support 508 may also provide(s) channels for gases supplied both tothe top of the plasma volume that is between electrodes, 505, as well asto the lower part of that volume that is between electrodes andsubstrate, 509. In some embodiments gases containing silicon and/orgermanium are injected into the plasma from injection manifolds withinthe electrode(s), 510 and 512. In some embodiments the gases injectedbetween electrodes and from within electrodes may contain hydrogen,oxygen, nitrogen, N₂O, inert gases, and gases containing silicon,germanium, or a metal such as zinc, tin, aluminum. It is noted that inthe configuration of FIG. 5 in some embodiments the gap betweenelectrodes, and that from electrodes to substrate, may be roughlyconstant along the length of such electrodes and both gaps are smallerthan either the width of such electrodes or their heights. In someembodiments, these gaps may be much smaller than the width of theelectrodes so that the potential in the plasma within such gaps isdetermined by the potentials of the two bounding surfaces which areclosest, which may be powered electrode and substrate, or poweredelectrodes, unlike some other configurations where multiple electrodesare farther from the substrate relative to their width. Further, suchgaps between electrodes and gaps from electrodes to substrate may becomparable in size. For example in some embodiments the gap between theelectrodes 501 and 502 may be between about 0.6 cm and 1.5 cm while thegap between electrodes 501 and 502 and substrate 507 may be betweenabout 0.5 cm and 1.5 cm. Such gaps may be chosen so that the ratio ofpower densities in the respective plasma regions—one region beingbetween electrodes and the other between electrodes and substrate—willbe optimal for the particular processing application. Some applicationssuch as deposition of low-hydrogen silicon nitride or low temperaturesilicon oxide or silicon nitride may benefit from higher power densitybetween electrodes than between electrodes and substrate. In exampleembodiments, the ratio of such power densities (Watts/cm3) would notexceed about 10 and in many cases would not exceed a factor of about 5.

Further, in a particular embodiment the gaps may be chosen so that thecross sectional area of the flow channel formed by the gap betweenelectrodes 501 and 502 is more than 50% of the cross sectional area ofthe flow channel formed by the gap between electrodes 501 and 502 andthe substrate 507. This helps assure that the gas stream does not cooldue to volumetric expansion as it flows from the one region into theother. When both power densities and channel cross sections, as well astemperatures of bounding surfaces are not much different, the gastemperature will not drop suddenly as the gas flows from one region intothe next. It should be noted that in some embodiments the lower edges ofthe electrodes, 501 and 502, are rounded with a curvature radius greaterthan or about 1 mm so that the gas flow coming from the region betweenthe electrode flows round such edges without forming recirculation flowpatterns. The minimum radius of curvature for avoiding suchrecirculating flow depends on the flow speed and density of such gas, aswell as the distance between the electrodes and the substrate. Forexample, at a gas pressure of about 4 kiloPascals and with a flow rateof about 4 SLM (Standard Liters per Minute) of gas per meter ofelectrode length and a gap between electrodes of about 8 mm and betweenelectrodes and substrate of about 8 mm the minimum curvature radius forthe edge may be about 1 mm in some embodiments. The maximum radius maybe approximately equal or slightly greater than the gap betweenelectrode and substrate in some embodiments. In some embodiments theradius preventing recirculating flows can be replaced by a facet ormultiple facets—bevels—that effectively serve the same purpose.

The range of gas pressures in some embodiments as illustrated in FIG. 5may be from about 200 Pascals to about 10,000 Pascals or any rangesubsumed therein. For embodiments in which dielectric materials aredeposited where compressive stress is required at or above about 100MegaPascals, the gas pressures may be in the range of from about 50Pascals to about 500 Pascals or any range subsumed therein. Forapplications such as passivation coatings for polysilicon or crystallinesolar cells where film stress should be low and ion bombardment of thesubstrate and growing film should be minimized, the pressure may be keptabove about 1000 Pascals (1 kiloPascal) in some embodiments. Wheresmaller gaps between electrodes below about 10 mm and between substrateand electrodes below about 10 mm are used the pressure may be in therange of from about 5,000 Pascals to about 15,000 Pascals in exampleembodiments or any range subsumed therein.

Total gas flow within a PGU per meter of electrode length may be in therange of about 200 sccm (Standard Cubic Centimeters per Minute) to 20slm in example embodiments or any range subsumed therein. Flows may bein the higher end of the range above about 2 slm for processes at higherpressures above about 1000 Pascals. Typical gas composition depend onthe particular application. Table I contains a list of some exampleapplications and their associated gas mixtures together with projectedranges for pressure and gas flows that may be used in exampleembodiments. Such ranges of pressures, gas mixtures, flows and AC powerlevels may apply to processes that may be performed using any of theconfigurations shown in FIG. 1-3 or 5-11 using any of the PGUs show inFIGS. 4 a-4 l or combinations thereof. In some examples, the processesbelow may be performed with less than all of the gases listed. Theexample pressure and gas flow below include any range subsumed in theranges listed below. These are examples only and other embodiments mayuse other gas mixtures, pressures and gas flow.

TABLE I TOTAL GAS FLOW (Standard Liters/ PROCESS GAS PRESSURE minute permeter of APPLICATION GASES (Pascals) electrode length) Deposition ofSilicon N₂, Si_(n)H_(2n+2), NH₃, Ar, 50 to 2000  0.1 to 5 Nitride havinglow He, SiF₄, NF₃, Hydrogen content. SiHCl₃, SiH₂Cl₂, An exemplary N2,SiH₄, Ar, He 100 to 300   0.5 to 3 embodiment of SiN deposition.Deposition of nano- Ar, He, H₂, SinH_(2n+2) 400 to 10,000  0.2 to 20crystaline Silicon for PV or LCD applications An exemplary Ar, H₂, SiH₄1000 to 4000   2.0 to 8 embodiment of nc- Si:H deposition Deposition ofAr, He, H₂, SinH_(2n+2) 400-10,000  0.5 to 20 amorphous silicon Anexemplary Ar, H₂, SiH₄ 1000-4000   2.0 to 6 embodiment of a-Si:Hdeposition Deposition of Silicon TEOS, TMCTS, SiH₄, 50-500  0.1 to 5Oxide with O₂, N₂O, Ar, He compressive stress Isotropic Etching of SF₆,CF₄, CHF₃, 500-15,000   1 to 20 Silicon Nitride CH₃F, Ar, CH₂F₂, (Si₃N₄at high rates C₂F₆, NF₃, O₂, C₄F₈, (>10,000 Â/minute) He, N₂, NH₃, CH₄,Cl₂, HCl Anisotropic Etching SF₆, CF₄, CHF₃, 50-300  0.5 to 5 of SiliconDioxide at CH₃F, Ar, CH₂F₂, high rates (>7000 C₂F₆, NF₃, O₂, C₄F₈,Â/min). He, N₂, NH₃, CH₄, Cl₂, HCl Deposition of CH₄, CnH_(2n+2), C₆H₆,1000-10,000    1 to 20 amorphous Carbon or C_(n)H₄, CF₄, C_(n)H_(2n+2),Diamondlike Carbon H₂, Ar, He Films Hydrogen Treatment H₂, Ar, He300-10,000 0.1 to 2 or Annealing of Silicon or Carbon- based filmsDeposition of ZnO O₂, N₂O, Z_(n)(CH₃)₂, 20-2000    1 to 20 He, Ar, H₂O,NO₂, dimethylzinc- triethylamine (DMZTA) Deposition of ZnAlO O₂, N₂O,Z_(n)(CH₃)₂, 20-2,000   1 to 20 He, Ar, H₂O, NO₂, Al(CH₃)₃, DMZTADeposition of low TEOS, TMCTS, SiH₄, 100-5000  0.1 to 2 temperature SiO2O₂, N₂O, Ar, He

The range of electrical power densities deposited in the plasmas in theregion between the powered electrodes and in the region between eachelectrode and the substrate may vary over a substantial range dependingon the gas pressure and the particular application desired. The activearea (in centimeters squared) for estimating the injected power densitywithin a PGU is approximately the sum of the area as projected on thefacing electrodes in the gap between the powered electrodes and theareas of the powered electrodes as projected onto the substrate. Thepower density parameter is calculated by dividing the total powerdelivered to a PGU using a source of RF, VHF, UHF, or combinationsthereof by the active area as calculated above. For higher pressures,above about 4,000 Pascals, it may be desirable to have at least about1.0 W/cm² up to about 10 W/cm². However, for gas pressures below about1,000 Pascals it may be desirable in some embodiments to have powerinjection less than about 3 W/cm² and possibly as low as about 0.1 W/cm²when the gas pressure is less than about 200 Pascals.

Another useful metric for RF, VHF or UHF power injection is the densityof power injection per cubic centimeter of plasma volume, perkilo-Pascal of gas pressure. This is in effect a power input permolecule or atom in the gas. Weakly electronegative or inert speciesdominated plasma can be stable at a value of about 0.1 W/cm3-kPascal ormore, but become unstable much below this value. Electronegative gasesrequire higher power densities to be stable. The processing applicationswe consider fall into roughly two categories—those that use ionbombardment as a primary process mechanism and those that rely almostexclusively on neutral species alone. For the former processes thedensity of power injection, Dp (W/cm3-kPascal) may be in the range ofabout 3 to 100 or any range subsumed therein. For the radical drivenprocess the range of D_(p) may be between about 0.1 and 10 or any rangesubsumed therein. The overall range for the power density parameter,D_(p), for these example processes is between about 0.1 and 100 or anyrange subsumed therein.

In an example embodiment illustrated schematically in FIG. 6, thesubstrate(s), 601, moves adjacent to multiple, closely spaced PGUs, eachone similar to the PGU embodiment illustrated in FIG. 5. Supporting thesubstrate adjacent its opposite side a support structure (which may be aneutral electrode), 602, may be connected to ground in some embodimentsthrough an impedance element 610 consisting of components such asinductors, capacitors, resistors which may be variable, or other solidstate devices such as diodes or varistors. Alternatively, it may not beconnected to grounded directly through components or may be groundedthrough a strap or straps that have some inductance. There may be anacceptable modest impedance to ground provided simply by the capacitancebetween a floating support pedestal or carrier and nearby groundedstructures such as chamber wall(s). Such structure serves as an anodefor the RF, VHF or UHF currents flowing from one or more electrodes.Typical total impedance from the neutral electrode 602 to ground may bein the range between less than or about 1 Ohm to about 10 Ohms or anyrange subsumed therein. In some embodiments the powered electrodes beingin pairs having roughly opposite voltages at any instant in time willconduct to the support structure roughly equal and opposite RF, VHF orUHF currents so that the net current to the neutral support structure issubstantially less than the current to either electrode. In this mannerthe voltage of the support structure and substrate may be kept smalleven though they may not be directly grounded due to the limitationsimposed by the mechanism that moves the substrate.

While other gas injection locations may be used in other embodiments,FIG. 6 shows an example pattern of overall gas flow from initialinjection to exhaust for a multi-PGU processing chamber according to anexample embodiment. Gas initially injected into the gap between poweredelectrodes. 603 and 604, of each PGU flows through a plasma discharge inthat gap towards the substrate until passing the electrodes where thegas flow splits into two streams that divert in opposite directions toflow between each electrode and the substrate or carrier for substratesthat is underneath it. Such flow pattern is without recirculation due tothe relatively narrow gap between powered electrode and substrate—thatmay be less than or about 1 cm, and the rounding of the bottom edges ofthe electrodes which may have radius of order 1 mm to as much as 2 cm.In some embodiments the rounding may be between about 3 mm and 6 mm whenthe pressure is between about 3000 Pascals and about 5000 Pascals andthe flow rate between about 1.0 to about 5 slm per meter of PGU length.The flow of gas continues under the electrodes until it passes by themto where the gas stream meets that from the adjacent PGU, and thesestreams combine to flow away from the substrate towards the exhaust,again without recirculation in the flow stream. The flow then continuesupward past the electrodes, 604, and past support structure, 605,diverting at the chamber wall, 606, where it continues to flow withoutrecirculation around the rounded corner of the support structure, whichmay be an insulating material to arrive at exhaust ports between thewall and the fixtures or standoffs, 607, for the support structure. Theavoidance of gas expansion cooling and recirculation as practiced inthese embodiments reduces formation of particulates in the gas phase forboth deposition and etching processes using certain chemistries, andimproves the resulting processes. There may be plasma present in thisgap between the electrodes of adjacent PGU which will reduce thetendency for forming deposits on the walls of such channel or reduce thetendency for such deposits to produce gas phase particles.

In some embodiments, as illustrated schematically in FIG. 7, liners 702can be used to cover surfaces 701 otherwise directly exposed to processgas. Such liners may be made of dielectric material or conductingmaterial or both. Liner thickness may be from 0.1 to 10 mm, with moretypical thicknesses from 1 to 5 mm. In some embodiments liner thicknessmay be varied according to position across the lined surfaces. In someembodiments liners may, over most of their area, be spaced asufficiently small distance apart from the electrode, such that plasmais not sustained in that small space. In example embodiments, that gapmay be between about 0.03 to about 5 mm or any range subsumed therein,depending on the gas pressure and power density, and may vary withposition on the electrode. At gas pressures above about 1000 Pascalsthis gap may be less than or about 1 mm in example embodiments. In thismanner the spatial distribution of the transmitted power density to theplasma may be modified—in some embodiments with the goal of making thepower density and plasma density more uniform. Such liners may have onlysmall areas of contact with the electrode surface in regions where thatliner is exposed to plasma. In example embodiments, such areas ofcontact may have dimensions less than the thickness of the liner tominimize variations in sheath potential and transmitted power density.In some embodiments the dielectric may be glass, quartz, AlON, aluminumoxide, silicon nitride or other such materials. In some embodimentsliners may be of conducting materials such as silicon, silicon carbideor other poor conductors that have such low electrical conductivity thattheir skin depth is comparable or larger than the thickness of theliner. Liners may also have thin coatings such as silicon dioxide,aluminum oxide or silicon which protect their surfaces from beingaffected by species generated from gases used in the process. Theseliners may cover the surfaces of an electrode and the surfaces of thesupport structure that might otherwise be exposed to the plasma or gasstream. Such liners may cover electrode surfaces facing the opposingelectrode within a PGU, facing the adjacent electrode of an adjacentPGU, or facing the substrate, 601, or all surfaces otherwise exposed tothe process plasma ambient. Such liners may be part of a singleintegrated structure, or be in segments, and may have one or more thanone layer covering one or more sides of the electrodes. Such linersconduct to the plasma the RF, VHF, UHF or microwave frequency currentsprovided to the electrode, and thereby inject current and power into theplasma. In embodiments where gas is injected from the electrode, itneeds to pass through such liner in order to reach the plasma. To permitsuch conduction of gas there may be holes in the liner. In someembodiments, the liner may be of porous material or there may bestructures or openings in the liner(s) such that the gas may conduct tothe plasma but very few ions and plasma fall directly onto theelectrode. In some embodiments such a structure eliminates any line ofsight from the plasma through the liner to the electrode, thoughobliquely angled holes may also be adequately effective.

Such liners may help to reduce the amount of heat conducted from theplasma to the electrodes as well as causing a hot surface to be presentadjacent to the plasma and process environment. Such hot surface mayhave substantial process benefits depending on the particular process.Such hot surfaces receive the deposits from the plasma, while theelectrodes may be at the same time kept cool so as to avoid problemswith mismatch in thermal expansion during operation. Such heatedsurfaces may be easier to clean off by an in-situ cleaning process andare less likely to cause deposited material to flake off and putcontaminants into the deposited film on the substrate.

For some embodiments with liners, the plasma density between theelectrodes relative to that between electrodes and substrate, may besubstantially modified by having different liner gaps or thicknesses inthose regions. Such liner gaps and/or liner thickness may be made todiffer by a factor of 2 or more, resulting in substantially different ACsurface potentials on the liner surfaces in the two regions. Likewise,power and plasma densities in both of these regions may differ fromthose in regions between electrodes and the outside bounding surfaces inembodiments having plasma in such regions. Relative RF, VHF, UHF ormicrowave power densities in these different regions of plasma are alsochanged by varying the relative liner thickness or gap sizes betweenelectrode and liner. In embodiments where liner(s) with dielectricproperties are used, these may become the outer plasma-bounding surfacesand the liner thickness may be used to adjust the relative powerdensity. Such dielectric liners may be made of materials that includedielectrics such as quartz or materials such as silicon or siliconcarbide. By making thicker those parts of the liner covering the sidesof electrodes facing each other, and making thinner those parts coveringthe sides facing the substrate, the relative power density and plasmadensity in the regions adjacent the substrate may be increased. Forexample, a quartz liner may be 2 mm thick in the areas facing theopposing electrode and 1 mm thick in the areas that face the substrate.This amount of liner thickness variation may substantially increase thepower density adjacent the substrate relative to that betweenelectrodes, even while the gaps between electrodes may be the same asthat between electrodes and substrate.

FIG. 8 illustrates schematically a gas injection manifold structure thatin some embodiments may be within an electrode, 811. Gases injected fromsuch a manifold may include either inert gas and/or process gases, suchas hydrogen, halogen, silicon, germanium or dopant containing gases.Such a gas injection manifold can also be used in other embodimentswithin a divider. The example embodiment illustrated in FIG. 8 includesthe option of controlling the distribution and gas mixture across thewidth of the electrode bottom surface. In the embodiment illustratedschematically in FIG. 8, gas is first introduced from separatelycontrolled supplies. 801 and 802, by ducts, 803 and 804, which passthrough both support structures and the actual electrode or divider, toupper reservoirs, 805 and 806, within the electrode. These channelstypically extend almost the full length of the electrodes and areconnected to the lower reservoir, 807. In some embodiments the channelshave much higher conductance along their length than the conductance tothe lower reservoir, 807, such that gas effectively fills the upperreservoir 806 much faster than the holes to the lower reservoir canempty it. The lower reservoir also typically extends along almost thefull length of the electrode or divider so as to be able to provide gasevenly along almost the full length of the plasma. In such manner themixture delivered to the lower reservoir from each upper reservoir isalmost exactly the same along the length of the reservoir. The lowerreservoir has small holes, 808, that distribute this gas into the volumeof plasma between that powered electrode and the substrate, 809, andsimilar holes, 813, for gas injection into leading to the space betweenelectrodes. The lower reservoir in an electrode may have a baffle orflow restrictor, 817, within it which reduce the gas conductance in thedirection parallel to the substrate motion. In this way the gasesinjected into the primary reservoirs, 805 and 806 will mix inproportions depending on the relative distances from the two primaryreservoirs, and depending on the total flow of gas to the two upperreservoirs. Gas coming through holes, 813, for example will be virtuallyentirely coming from gas supply 801 via primary reservoirs, 805, due tothe minimal diffusion of gas from supply 802 which fills upper reservoir806. In this manner the gas mixture flowing from the rows of holes atincreasing distance from reservoir 805 will have a decreasing proportionof gas from primary reservoir 805. There may be such small holesdistributed in some manner over nearly the full width of the reservoir,thus introducing gas into the plasma over a substantial proportion ofthe width of the electrode. In some embodiments gas may also be injectedfrom this reservoir into the volume between electrodes 812. Such gas mayin part come from a separate supply of gas, 814, via an input channel toa reservoir in the insulating support, 815, and thence be injectedthrough small holes, 816, into the plasma between electrodes, 812. Thesubstrate is supported by a support. 810, which is also the neutralelectrode that may be connected to ground by means previously described.The upper reservoirs may in some embodiments be connected to the lowerreservoir near its opposite sides through holes or narrow channels orbaffles. The lower reservoir may in some embodiments be a connectedvolume, and may in some embodiments, be divided into sections which mayextend the length of the electrode with channels between them so thatgas from the two upper reservoirs can mix in varying proportions in thedifferent sections or regions of the lower reservoir. In someembodiments gas injected into the upper reservoirs, 805 and 806, flowsalong the length of these reservoirs as it more slowly flows into theadjacent part of the lower reservoir, 807. Gas from the two upperreservoirs then mixes within that lower reservoir in proportions thatwill vary with the position—specifically proportions that vary almostexclusively in the direction of the width dimension of the lowerreservoir and of the electrode. Whatever the proportions of gases fromthe two upper channels that is in the mixture at any of the small holes,808, will be the mixture delivered to the plasma by that hole. In thismanner gas that is a mixture with proportions of gas from each upperreservoir that vary with the relative gas conductance from the two upperchannels will be delivered to the plasma. In such manner the gas mixturedelivered to the plasma may be made to be almost precisely constantalong the length of the electrodes, so that the process is substantiallyconstant in rate and properties along the length of the electrodes.

FIG. 9 schematically illustrates an example embodiment of a PGU thatincludes a grounded electrode, 901, and a powered electrode, 902.Plasma, 903, is generated between powered and grounded electrode by theapplication of an AC potential to the powered electrode, and plasma,904, between powered electrode and substrate. Such plasmas are largelyindependent in power density, each being dependent on the gap betweenthe powered electrode and the opposite surface, and the relative ACpotentials across the gaps. A larger gap increases the electricalresistance of the plasma and thereby reduces the current density flowingacross such gap. Therefore, the relative size of the gap between poweredelectrode and substrate versus the gap between electrodes willdetermine, in part, the proportion of the power supplied to poweredelectrodes that is actually deposited in each of the plasma regions. Theproportion of power supplied to the different plasma regions may also bevaried by the use of dielectric liners with different thicknesses, andgaps to liners for areas facing the substrate versus facing the groundedelectrode. The impedance 905 from the neutral electrode to ground willalso have an influence on the division of the RF, VHF, UHF or microwavecurrent coming from the powered electrode and conducting to the groundedelectrode or to the substrate. Should the impedance to ground of theneutral electrode be high it will cause more current to flow to thegrounded electrode versus the substrate resulting in a denser plasma 903in the region between electrodes, versus that adjacent the substrate,904. In some embodiments a portion of the grounded electrode, 901, maybe a dielectric material such as quartz or ceramic so that there is lesslikelihood of plasma forming in the gap between the grounded electrodeand the substrate. In example embodiments, the gap between the tip ofthe grounded electrode and the substrate may be from 0.1 to 5 mm, or anyrange subsumed therein. In some example embodiments, this gap may beless than about 0.5 mm. There may be injection of inert gas from thebottom of the grounded electrode in some embodiments as well asinjection of gas from a manifold within the powered electrode.

In an example embodiment illustrated schematically in FIG. 10, there aremultiple, closely spaced PGUs, each one similar to the PGU embodimentillustrated in FIG. 9. The gas flow in this embodiment starts in theregion (or gap), 1001, between the electrodes, 1006 and 1007, in adirection toward the substrate surface, and then diverts upon passingthe powered electrode 1007 so that a substantial majority of the gasflows in the gap, 1002, between the powered electrode and substrate,which may be between about 5 nun and 10 mm in example embodiments. Thisis due to the much smaller gap 1008 between the tip of the groundedelectrode 1006 and the substrate 1009 that restricts the flow under thegrounded electrode. The flow then diverts again after passing under thepowered electrode and flows along the surface of the powered electrodeaway from the substrate surface in region (or gap) 1003 towards theexhaust. In embodiments where there is a similar PGU on both sides ofthat shown, the upward flow adjacent the powered electrode is between itand the grounded electrode of the adjacent PGU on the right side. Inthis case, if the gap between the adjacent PGU were comparable to thegap 1002 between the powered electrode and the substrate, there would beplasma generated as well in gap 1003, which would have a comparablepower density. In some embodiments the gap between the PGU shown andthat on its right would be slightly larger than the gap 1001 betweenpowered electrode and the grounded electrode on its left. In such anembodiment the power density in gap 1003 on the right of the poweredelectrode may be less than in gaps 1001 and 1002. In this case the gasflowing away from the substrate may be moving through plasma with lowerpower density than in the earlier phases of its flow. Such power densitymay be no less than about 1/15th that in the gap to the substrate insome embodiments. After flowing past the electrode 1007 and the support1005 the gas reaches channel (or region) 1004, above the support 1005.This channel leads to an exhaust port from the chamber and may also haveplasma within it. In some embodiments an auxiliary power source mayprovide power to sustain the plasma in region 1004 or coupling thoughthe support structure from the electrode may be adequate to do so. Thus,the flow of the gas in embodiments as shown in FIG. 10 is essentially ina circuit as shown by the arrows—around the powered electrodes, and thenthe support and out of the chamber. An etching gas may also beintroduced near the exhaust yet inside the chamber so that depositingspecies may be converted to strongly volatile species so thatcondensation in pumping manifolds or valves may be avoided. The flowadjacent the substrate surface is substantially in a single directionwhich in some embodiments may be in the same direction as the movementof the substrate. The gas flow as shown moves around the rounded edgesof electrode, 1007, and support structure, 1005, with radii of curvaturebetween about 1 and 10 mm such that there are no recirculation patternsin the bulk gas flow as it flows from one region to another. Further,for some embodiments, any changes in the cross sectional area due tochanges in the gap dimensions, as the gas flows from one region to thenext should preferably kept less than a factor of 2. This helps reducegas cooling and particle growth due to expansion. Maintaining a high gastemperature helps reducing particle growth and contamination of thesubstrate.

In the example embodiments described above, the cross-sectional shape ofthe electrodes and dividers have a substantially planar surface both inthe gap between elements and the region facing the substrate surface.Additional embodiments can employ other shapes. FIG. 11 schematicallyillustrates an example embodiment utilizing electrodes with a curvedcross section. The shape of the curved electrodes 1101 and 1102 may addadditional benefits from some processes by concentrating the powerdeposited in the plasmas in to a small region 1103 and 1104 where thegap between electrodes, 1101 and 1102, to the substrate, 1105, is thesmallest. The rounded shape meanwhile may retain the benefit ofpreventing recirculation in the gas flow path.

Other embodiments may use other shapes for the PGUs. However, exampleembodiments using other shapes may still maintain some or all of thecharacteristics described above, including small electrode width andheight dimensions relative to the length; small gap between facingsurfaces of electrodes and dividers within a PGU; separatelycontrollable plasma power densities in regions adjacent the poweredelectrodes; and electrode shapes and gaps configured to prevent gasrecirculation.

FIG. 12 illustrates aspects of electrode and liner spacings andsubstrate support as found in example embodiments wherein liners areused to cover surfaces of electrodes otherwise in contact with theplasma. The electrodes, 1201, being made from conductive material, areseparated by a small distance, 1204, from the liners, 1203, which insome embodiments are dielectric material such as quartz. This liner maybe gas permeable so as to allow injection into the plasma from theelectrode(s). Example liner thickness may be between about 1 mm andabout 5 mm or any range subsumed therein, which may be different forsides facing the substrate from their thickness over sides facing otherelectrode or divider. The plasma is typically formed between theelectrodes only in the gaps, 1204 and 1205, and not in the small gap1202 between electrodes and adjacent liners. In example embodiments, themaximum allowable electrode-liner gap, 1202, to avoid formation of aplasma depends primarily on the gas pressure and on the power densitylocally injected into the plasma. At gas pressures below about 0.1kiloPascals and at power densities below 1 W/cm2 the gap. 1202, may evenbe as large as 2 to 5 mm without causing a plasma therein, though thismay not be practical due to the large voltage drop between electrode andouter surface of the liner. Higher gas pressures, above about 1kiloPascal, may require gaps less than 1 mm, especially at power levelsof 1 W/cm2 or more to avoid sustaining a plasma therein. Pressure aboveabout 3 kiloPascals may require an electrode-liner gap less than 0.5 mm.In the disclosed device this gap may be at less than about 0.05 mm ormore in order to provide desired thermal insulation between plasma andelectrodes and to increase the temperature of the liner to above 100° C.everywhere over its surface in some embodiments. This also serves toincrease the minimum gas temperature in the plasma region, 1204, togreater than about 100° C. This higher gas temperature tends to beparticularly helpful in avoiding growth of gas phase nano-particles inthe plasma regions and helps to reduce defects when growing silicon orsilicon-based films. The gap 1205 between liner's outer surface and thesubstrate may be between about 5 min and as large as 20 mm, though moretypically at gas pressures above about 1000 Pascals, the gap to thesubstrate is often no more than about 15 mm. In some embodiments wherethe process pressure may be above about 5 kiloPascals the maximum gapfrom liner surface to substrate may be less than about 10 mm. The gapbetween facing liner surfaces, 1202, is typically in roughly the samerange as that between liner and substrate but in some embodiments may beslightly larger due to the constraint of avoiding rapid expansion in thecross sectional area of the flow channel for gas.

The substrate, 1206, may in some embodiments rest on a carrier, 1207,which is a good electrical conductor, which may in turn rest on or withsmall gap, 1208, to a pedestal or support structure with a small compleximpedance 1210 to ground. The magnitude of such impedance may be lessthan about 10 Ohms in many embodiments to avoid plasma discharge fromthe carrier. The small gap, 1208, may be associated with a transportsystem that moves the carriers relative to the support, 1209. In thiscase the capacitance between carrier and support may be very high,reducing the build up of electrical potentials on the carrier when RF,VHF or UHF currents are conducted to it from powered electrodes of thePGU. Particularly in cases where the substrate moves relative to thePGU, it may be difficult to provide a good electrical ground on thesubstrate carrier, but a very small gap, 1208, which may be less than afew millimeters will result in high capacitance to ground and lowresulting RF, VHF or UHF impedance. If the AC potentials of theelectrodes, 1201, are roughly equal and opposite, then the netcapacitive current to the substrate or carrier will be minimized and theelectrical potential of the carrier or substrate will be minimized.

In other embodiments, there may be AC power provided to the substratesupport and/or the carriers for the substrates. In such case there maybe additional ion bombardment of the substrate which in someapplications is beneficial.

In some embodiments, universally high gas temperature or avoidance ofelectrode heating may not be important, and thus liners on electrodesmay not be used in some embodiments. In many of these cases the limitsstated above for the gaps between liner surfaces, or gaps from linersurface to substrate would apply equally to the gaps between facingsurfaces of the electrodes, or between electrode surface and substrate,in the absence of a liner. Both such gaps might be between about 5 and20 mm or any range subsumed therein in example embodiments.

One example application for the example embodiments described above isthe deposition of thin films of nano-crystalline silicon (nc-Si:H) forphotovoltaic cells. It is desirable to reduce the cost of manufacturingsuch cells and provide higher efficiency for conversion of light toelectrical energy. In order to meet such requirements the defect levelsin the silicon may need to be less than or about 2 1016/cm³. In theevent deposition of thin films of silicon having such defect levels canbe achieved with excellent uniformity across an entire substrate,photovoltaic efficiencies of 13% or better might be achieved in cellshaving multiple absorber layers with different absorption bands.

In some cases, the cause of high defect levels in depositednano-crystalline silicon may in part be due to the incorporation oflarge numbers of clustered microscale silicon particles into the growingfilm. In some plasma reactors where gas temperatures are high, growthrates of small silicon particles may be much smaller. However,deposition systems for nc-Si:H that utilize a “showerhead” or otherinjector may have a relatively cold surface—which may be less than orabout 60 Celsius in some reactors. This may cause the gas to have higherformation rates for particles that ultimately are incorporated into thefilm resulting in reduced Photovoltaic efficiency. In exampleembodiments of the present invention, the operating temperature ofsurfaces in contact with the plasma may be maintained at 100 C or moreby using hot liners covering the electrodes that are spaced from theelectrode surface to reduce heat conduction to the cooled electrode. Byproviding hot surfaces adjacent the plasma, hot gas temperatures may besustained throughout the plasma region. Because gas phase particlegrowth is reduced, example embodiments may be operated at high powerdensity and achieve higher deposition rates, while maintaining lowdefect levels in the deposited film. For example, deposition rates insome embodiments may exceed 4 nanometers/second. Other embodiments mayuse other configurations to maintain temperatures at or above 100 C forsurfaces adjacent the plasma to reduce particle growth in the gas phaseand thereby improving the PV efficiency.

In some embodiments, such as those shown in FIGS. 4 a-4 l, the substratesupport may be either a neutral electrode, while in other embodimentspower may be provided to the substrate support and/or the carriers forthe substrates. In such case there may be additional ion bombardment ofthe substrate which in some applications is beneficial. In someembodiments, use of a dc or low frequency bias on the substrate may beuseful in reducing the defect level of the silicon, or increasing thedensity of the deposited film.

In some embodiments a small gap is maintained between the poweredelectrodes and the substrate. In example embodiments, this gap may bebetween about 5 mm to 15 mm or any range subsumed therein. Because it isimportant to precisely control the gap between the electrodes andsubstrate in order to avoid non-uniformities in the deposited film, itmay be useful to employ aligners near to a PGU, or a pair of parallelplate electrodes, that keep the substrate at the desired gap relative tothe electrodes. It may be useful to have aligners at regularintervals—typically much less than the length of a substrate—along thepath of the substrate both before and after a processing region tocontrol the substrate-to-electrode spacing, without adversely affectingthe quality of the film deposited. Such aligners may be separated from aPGU, but elongated like dividers or grounded electrodes in spanning thewidth of the substrate, perpendicular to the direction of motion, andproviding a flow of gas, as shown in FIG. 4 h or 4 j. The gas flow fromthe end adjacent the substrate prevents the substrate from touching thenearby surface of the aligner. Alternatively, the aligner may have oneor more “arms” which may be rigid or have some ability to flex, and eachmay have one or more isolated pads at the end whose surfaces are largeenough—usually greater than about 5 square centimeters—and have vents inthat surface as a source of inert gas. Such arms and pads are configuredand positioned at a small distance—typically less than about 2millimeters—above and/or below the plane of substrate motion, to causethe substrate to move through the electrodes or PGU at the desireddistance. Aligners that are sources of gas with no pumping may beadjacent the side of the substrate whereon processing is to take place,or adjacent both sides of the substrate. Aligners may also have vacuumapertures in the pads so that they act effectively as “gas bearings”,though in this low pressure environment the larger pad area is helpful.

In an example embodiment, a method for depositing silicon layers to forma portion of a photovoltaic cell may be provided including some or allof the following features (or any combination thereof):

-   -   a. Providing at least three sets of PGUs wherein the first set        includes at least one PGU and the third set includes at least        one PGU;    -   b. Wherein the second set is between the first and the third set        and includes a number of PGUs greater than the number of PGUs in        the first and third sets;    -   c. Moving a substrate linearly below the three sets of PGUs;    -   d. Depositing a first layer of doped silicon using the first set        of PGUs, wherein the silicon has a first type of doping;    -   e. Depositing a second layer of intrinsic silicon over the first        doped layer using the second set of PGUs, wherein the second        layer is thicker than the first layer,    -   f. Depositing a third layer of doped silicon over the second        layer using the third set of PGUs, wherein the third layer has a        second type of doping.

One example application is the deposition of the multiple layers ofsilicon-based films for a photovoltaic device. In this example, a dopedlayer may be deposited first, then an intrinsic absorber layer may bedeposited and finally another complementarily doped layer may bedeposited. Example embodiments may be used for deposition of all threelayers in sequence at the same time in the same apparatus and even inthe same chamber.

In example embodiments, a conveyor, web or other moveable transport orcarrier may be used to move the substrate below the PGUs. Such motion isoften linear, though it may be curved for continuous band substrates.Such substrates may move in a path such that they describe segments thatmay be part of a cylinder.

In example embodiments, as shown in cross section in FIGS. 3-12, thePGUs may be arranged so that the long sides of adjacent elements ofneighboring PGU are approximately parallel and narrowly spaced along thedirection of substrate motion. Cross sections of the electrodes may beroughly rectangular in example embodiments as shown in the same Figures.

In these example embodiments, each PGU may generate a plasma in volumesadjacent elements of that PGU. The plasma in this region issubstantially controllable with the power provided to AC poweredelectrodes of this PGU. In some examples, such electrodes may be atexcitation frequencies such as in RF or even VHF bands and may couplethat power into the plasma mainly through displacementcurrents—capacitive coupling. In some examples, the coupling of powerfrom the PGU into the plasma may be principally inductive where someelements of the PGU include one or more turns of a coil. In someexamples, the power is in the UHF or microwave bands and the coupling ofpower into the plasma may be as surface waves which are both inductiveand capacitive in their nature. In example embodiments, processing inthis region may be substantially a product of the plasma generated byelectrical power injected via the PGU. Other PGUs may be used in otherembodiments.

In FIG. 13, example embodiments are shown having multiple adjacent PGUswithin a single chamber, wherein separately controllable gas or mixtureof gases are supplied from gas supply systems, 1321 to 1325, to PGUs1301 through 1305, respectively in the chamber, permitting differentprocesses to be performed simultaneously within the chamber on asubstrate by different PGUs or groups of PGUs. In some embodiments, theprocesses performed by PGUs 1301 and 1302 may be substantially the sameon the substrate using separately controllable gases or mixtures ofgases, 1321, and 1322 respectively, which in such embodiments aresimilar or identical. In some embodiments, the gas mixtures to the twomay contain the same components but proportions may differ slightlycausing only the rate of the process to differ between the two. In theseembodiments, the PGU 1303 may or may not utilize AC power to produce aplasma, but uses a flow of only inert gas which causes no process to beperformed on the substrate within the region of this PGU. However,because gas is injected within each PGU and is removed via an exhaustport, within or adjacent that same PGU, such region of inert gas mayserve to isolate processes in PGU 1304 and 1305 from the gaseous speciesin PGU 1301 and 1302, and vice versa. For example, gas injected from gassupply 1321 into PGU 1301 may be exhausted via ports 1331 and/or 1332,and gas injected into PGU 1304 from supply 1324 may be exhausted viaports 1334 and/or 1335.

One example is the case where PGUs 1301 and 1302 deposit a heavilyphosphorus doped silicon layer and PGUs 1304 and 1305 deposit undopedintrinsic silicon layers. In this example, the direction of some of thegas flow in PGU 1303 may be from right to left toward 1301 and 1302 andaway from 1304 and 1305 so as to oppose any flow or diffusion ofphosphorus containing gas species from PGUs 1302 into PGU 1304. Inanother example, there may be etching using fluorine containing speciesin PGUs 1301 and 1302 while there are deposition processes in PGU 1304and 1305.

In an example embodiment, a substrate, 1311, entering the chamber may besubjected to flow of a purge gas 1326 supplied to injectors over thesurface of the substrate, 1311, while a substrate may be subjected topotentially different gas, 1327 prior to exiting the chamber. Such purgegas, along with other gases ambient outside the PGU may be pumped byexhaust ports, 1313. Exhausts 1328 for gases provided within each PGUmay be separate. Though they may flow to a common vacuum pump, inexample embodiments, they do not allow species out one exhaust duct todiffuse back into any other process region.

In FIG. 14, a cross section of an example chamber is shown with elementsof two or more PGUs, 1401 and 1402, having a common support, 1405, for alarge substrate, 1403, which maintains a very small, and controlled gap,1404, from the PGU to the support. The substrate support has internalchannels 1405 connected to a supply of gas 1407 that terminate inapertures at the substrate supporting surface having at least onedimension less than about a millimeter—for introducing gas into the gap,1404. There are other channels 1406 that are in the substrate supportthat are connected to a vacuum pump 1408 or other exhaust which alsoterminate in apertures on the surface of the substrate support.

Shown in FIG. 15 is an example embodiment for a substrate supportpedestal having linear apertures for gas injection and exhaust. Shown isa substrate, 1501, supported on a pedestal, 1502, by gas injectionsupplied from a network of channels, 1503. Gas from the channels, 1503,is injected into the space between substrate and support that has aheight, “d”. The gas injection is around small baffles, 1505, whichdistributes the gas into the space with height “d”. The apertures forgas injection are less than about a millimeter in width but sufficientlylong to provide gas somewhat uniformly into the space between supportand substrate. Similarly, the gas is exhausted from this space betweensubstrate and support in this embodiment through larger channels, 1504,which are covered by baffles, 1506. The baffles are elongated such thatapertures on the support surface are elongated but narrow, less thanabout a millimeter, which provide sufficient pumping speed to exhaustgas from the space between substrate and support. By maintaining suchsmall apertures, and keeping the gap, d, less than a millimeter the gasin the space between substrate and support is prevented from forming aplasma, due to electrical fields from the PGU.

FIG. 16 shows an alternative embodiment of a substrate support 1602having baffles 1605 and 1606 which are porous conducting material suchthat electrical fields coming from the PGU do not penetrate into thechannels, 1603, which are sufficiently large to permit good conductancein exhausting the gases from the space between substrate and support.Avoiding electrical fields in such channels prevents plasma from formingin exhaust channels 1603, where gas pressures are generally smaller thanin the space between substrate and support. In this case, the high gasflow conductance of the porous plug material causes there to be a strongresponse in the average gas pressure between substrate and support whenthe gas conductance between the injector holes and the porous exhaustports changes due to the gap between substrate and support eitherincreasing or decreasing. Note that the conductance for gas flow in theviscous regime between two surfaces varies at least as rapidly as thesquare of the gap between them.

Such example substrate supports as shown in FIGS. 14-16 may be used forprocessing large substrates since they permit maintaining a highlyconstant gap between the elements of the PGU and the substrate. Controlof the gap to a high precision and uniformity is achieved by thedisclosed substrate support since there is a natural restoring mechanismto prevent the gap between support and substrate from varying. Thismechanism works as follows: gas pressure average between substrate andsupport decreases rapidly when the gap between them increases due to theconductance increase between gas inlets and exhaust in the support. Thisdecrease in gas pressure between substrate and support causes thesubstrate to be driven back down toward the support due to the higherprocess pressure within the PGU above the substrate than the gaspressure between substrate and support. When the gap between support andsubstrate decreases that conductance decreases rapidly causing theaverage pressure between support and substrate to increase pushing thesubstrate so as to increase the gap between support and substrate. Thegap between substrate and PGU elements is small—between about 5 mm and15 mm—and the local power density of the plasma is highly dependent onthis gap. If the gap between an AC powered electrode and the substratevaries by 10% over the length of the electrode or from one AC poweredelectrode to another, the resulting power density non-uniformity may be20% or more, causing process non-uniformities of the same order or evenworse. In case there are dielectric liners on the AC powered electrodesthe plasma non-uniformity will be mitigated by the high impedance(capacitive reactance) of the gap to the dielectric liner and the lineritself since higher current AC current densities passing through theliner will result in larger voltage drops across the liner and hencelower voltage on the plasma-facing surface of the liner.

In example embodiments, to achieve adequate process uniformity, U—whichfor many processes must be better than +/−5%, [where U=(max−min)/(twicethe average)], the gap from AC powered electrodes to substrate may bemaintained to about 2% or less. In some embodiments where processuniformity is of order +/−1%, the size of the gap over an AC poweredelectrode may be controlled to be better than about +/−0.5%. For a gapfrom AC electrode to substrate which is about 10 mm, the gap may varyless than about 0.2 mm in most cases, and may vary by less than 0.025 mmwhen the gap is about 5 mm and the process control is better than about+/−0.5%.

In FIG. 17 is shown an example embodiment of a PGU in which plasmaformation is by inductive coupling via AC current flow in electricallyconducting windings, 1705, in which currents, 1707 and 1708, havingopposing directions flow in adjacent support structures, 1701, and 1702respectively. The source of such AC current is the supply, 1706, andcurrents having passed through the windings 1705 are returned to groundvia connection 1703. Such current in the windings produces rapidlyvarying magnetic fields in the spaces around the support structureswhich induce electric currents, 1709 and 1710, sustaining the plasmasthat are formed in the regions between such structures and thesubstrate, 1507, which moves past such structures. Gas may be injectedthrough small holes 1704 into the space 1711 wherein plasma is alsosustained. Such inductive coupling may generally be at If or RFfrequencies for such large windings as would be used with structures,1701 and 1702, that have lengths greater than about 35 centimeters forprocessing substrates of roughly 30 centimeter width or greater. Processchambers may have variable numbers of PGU and PGU may be of varyingwidths. For applications such as silicon deposition on photovoltaicpanels which are roughly a meter in width and a meter and a half inlength, in some embodiments there may be from about 5 to as many asabout 100 PGU in a single chamber. Each AC powered electrode or coilwinding structure may be roughly from about 3 centimeters in width to asmuch as about 30 centimeters and PGU may be from about 4 centimeters toabout 60 centimeters.

FIG. 18 illustrates an example embodiment with power splitting betweenelectrodes. In FIG. 18 is shown a physical and electrical model of theequal splitting of RF or VHF power injection from a generator, 1801,through an impedance matching network, 1802, and then through roughlyequal inductances, 1803 and 1804, to electrodes, 1806, which are mountedon a ceramic support, 1805. Each electrode is covered by dielectricliners, 1807. The splitting of the power by the two inductors isfacilitated and stabilized by the presence of the dielectric linerswhich act as series capacitors, 1811, in the current flow path from theelectrodes to the plasma. The RF or VHF current from the electrode afterpassing through the liner moves through the bulk plasma 1808 which hasbeen successfully modeled as a series combination ofcapacitor-resistor-capacitor and then through the capacitance 1815 tothe support. The capacitors representing the sheaths at the surface ofthe liner and the substrate, and the resistor representing thecollisional losses of electrons carrying the current through the bulk ofthe plasma. Indicated in the figure are sheath capacitance, 1812,adjacent outer surfaces of the liners whose magnitude, in reality,varies with RF phase and ion current density of the sheaths that are incontact with the plasma. Such a sheath, 1814, is also present adjacentthe surface of the substrate or holder thereof. Between these sheaths isthe “bulk” plasma which has equal densities of negative and positivecharges. This bulk has an effective resistance, 1813, which representsthe resistance to motion of plasma electrons due to collisions with thegas as they carry the RF or VHF current between electrodes andsubstrate, 1809. There is also a grounded pedestal below the substrate,1810, which has a finite gap to the substrate, or if the substrate ismainly a dielectric material, to any conducting material on its surface.Such gap and, where present, the dielectric of the substrate comprise afurther capacitance from substrate or a conducting surface material tothe grounded pedestal, 1810. Sheath capacitance varies inversely as thesheath thickness which depends on plasma characteristics such as theplasma potential and ion current density. Sheath thickness (Child's lawfor collisionless sheaths provides roughly the correct scaling forcollisional sheaths) decreases approximately as the square root of thecurrent ion density and increases as the ¾th power of the potentialdifference. The sheath thickness also varies with the RF or VHF phase sothat the sheath capacitance is not constant in time.

For deposition of silicon for thin film photovoltaic applications,plasma operation at gas pressures above about 1000 Pascals reduces theamount of power going to the sheaths and therefore reduces the ionenergies. This greatly reduces ion penetration into the film, therebyreducing defects in the silicon and improving PV efficiency. Increasinggas pressure in the discharge also increases the power going to theelectrons and ultimately the efficiency of dissociation of feed gas intoneutral reactive species. In an example embodiment, power efficiency ofstripping of organic polymer by an oxygen plasma improves linearly withincreasing gas pressure above about 600 Pascals. It is believed thatprocesses dependent on production of neutral radicals may improveapproximately linearly with increasing gas pressure above about 500Pascals in example embodiments. In addition, as the gas pressureincreases to about 4000 Pascals undesirable effects including ion damageto the film may decrease to near zero, even at excitation frequencies inthe RF band as low as about 3 MHz.

In order to design the liner characteristics and choose the inductors tomake the splitting work best, the plasma reactances and resistancesshould be understood for a range of plasma conditions. Shown in Table IIare the ranges of impedances of the sheaths and bulk plasma for somepressure conditions that may be used in example embodiments. Theelectrical impedance of the discharge at a gas pressure of between 1000Pascals and 5000 Pascals shows two major effects associated with theimproving efficiency power transfer to electrons and reduced ion energyat higher pressures. First, the thickness of boundary layers—sheaths—atthe electrode and substrate surfaces are small, causing the sheathcapacitances to be large and the reactive part of the dischargeimpedance to be small.

For gas pressures above about 1000 Pascals the plasma resistivity ishigh due to the higher electron-neutral collision frequency and thelower density for electrons in the higher pressure plasma. (Plasmaresistivity is inversely proportional to the electron density anddirectly, linearly, proportional to the gas density). This means thatthe electrical resistance of the plasma is large. The electron densityis between about 109 to about 5×109 per cubic centimeter. Therefore, theplasma resistivity for the higher pressure case—greater than about 1000Pascals—is between about 10,000 Ohm-centimeters and about 200,000Ohm-centimeters. Assuming about a one centimeter gap, this results in aresistive impedance for a 0.25 meter squared electrode area betweenabout four (4) Ohms and about eighty (80) Ohms.

Above about 1000 Pascals the sheath thickness may be between about 0.2millimeters and about 1 millimeter. This means that for a single sheaththe capacitance per square centimeter is between about 1.2picofarads/cm2 and about 6 picofarads/cm2. Discharge reactiveimpedances, unlike resistive impedances, are dependent on the excitationfrequency—inversely proportional to frequency. For an operatingfrequency of 13.56 MHz the single sheath reactive impedance is betweenabout 10,000 Ohms per centimeter squared and about 2,000 Ohms percentimeter squared. However, for this plasma there are two roughly equalsheaths in series so one must double the single sheath reactance. Thus,the plasma reactance is between about 4,000 Ohms per centimeter squaredand 20,000 resulting in a plasma reactive impedance for a 0.25 metersquared electrode of between about 1.6 Ohm and about 8 Ohms.

If the liner has a gap from the electrode surface of about 0.25millimeters and the thickness of the liner to be about 3 millimetersthen the impedance of the liner at 13.56 MHz is about 14,000 Ohms percentimeter squared. This is in series with the reactive and resistiveimpedance of the discharge (see FIG. 18) and results in between 70% anda 350% increase in the reactive impedance of the high pressuredischarge. For a 0.25 meters squared liner area the total reactance thenis between about 7 Ohms and 12 Ohms—which is a much larger fraction ofthe resistive impedance of the discharge—helping to stabilize the plasmaspatial uniformity. The sheath reactance then is a much largerfraction—nearly equal in some cases to the resistive impedance. If glasssubstrates are used that are 3 mm thick then the reactance is increasedby 10,000 Ohm per centimeter squared to a range of about 24,000 Ohm percentimeter squared to 48,000 Ohms per centimeter squared, morecomparable to the resistive impedance.

Thus, in the high gas pressure discharge the resistive impedance isusually greater than the reactive impedance. If the excitation frequencyis increased to 40 MHz or above, it would further reduce the sheaththickness and the reactive impedance by a factor of several or moreresulting in even greater dominance of the resistive impedance over thereactive. It is believed that the energy transfer in this discharge isvery predominant to the electrons in the bulk of the plasma. Because atmodest power densities—less than a few Watts per centimeter squared—theelectron energy distribution in the high gas pressure case is stronglypeaked at lower energies, this energy goes mainly to dissociation ratherthan ionization, further improving efficiency for generation of speciesfor thin film deposition.

TABLE II Discharge Impedance - Discharge Impedance - no Liner with LinerDischarge Resistivity Reactance per Reactance per Conditions (Ohm-cm)square cm Resistivity square cm High Pressure 10,000 to 4,000 to 10,000to 18,000 to Discharge 200,000 20,000 200,000 34,000 (1000 Pascals to5000 Pascals)

In example embodiments, the aim of having roughly equal inductors inseries with the electrodes and their plasmas is to equalize the RF orVHF current to the electrodes and sustain the plasmas adjacent the twoelectrodes at approximately equal power densities and processing ratesof the substrate. The circuit with inductors splits the RF or VHFcurrent to the two electrodes and their plasmas. If there were no linerson the electrodes, then a greater density of one electrode's plasmawould increase the capacitance of its sheath and decrease both itssheath reactance and the resistance of its bulk region, so that thetotal impedance of the electrode and plasma would decrease. This wouldcause more of the current to go to that electrode and less to go to theother, making the power distribution to the electrodes and their plasmasmore unbalanced. However, when electrodes have the liners, whosethickness and dielectric constant are such that they have capacitancesless than, and reactances greater than those of the sheaths (undernormal plasma conditions) the splitting of the current between theelectrodes is stabilized. With the liner, if one plasma becomes denser,and begins to draw more current, the substantial reactance of the linercauses a larger voltage drop across the reactance of that liner, and thevoltage on the outer surface of that liner decreases. This, in turn,decreases the current through that electrode's plasma, decreasing theplasma density at that electrode. This self-stabilizing feature worksbecause the liner provides a suitable and sufficient capacitivereactance. Roughly, one chooses the value of the inductance for eachbranch of the splitter so that the inductive reactance of each cancelsthe combined series capacitive reactances of the liner and sheaths inthe lowest density plasma condition, or for no plasma. Then, as theplasma becomes more dense the sheaths at the electrode and substratebecome thinner, increasing their capacitance and decreasing theircapacitive reactance. This causes the total reactance (the sum of theinductive reactance which is positive and the capacitive reactance whichis negative cancel each other out at resonance condition) through thatelectrode, which is inductive, to increase substantially, whilereactance through the other electrode decreases roughly equally. Suchchanges in reactance are greater than changes in plasma resistance,thereby causing more current to pass through the electrode having theless dense plasma—this is stabilizing for the splitting of power betweenthem. For example, for 13.56 MHz RF power, to properly stabilize thesplitting of the current the capacitance of the liner should be fromabout 0.5 picofarad per square centimeter to about 1.5 picofarads persquare centimeter. As the frequency of the exciting current for theplasma increases, the liner thickness—and therefore itscapacitance—should be chosen to decrease less than linearly with theincrease in the frequency. So at 80 MHz one might have a range fromabout 0.2 picofarads per square centimeter to about 0.6 picofarads persquare centimeter. The value of the inductors, 1803 or 1804, would thendepend on the total capacitance of the liners which would also depend ontheir areas facing the plasma, as well as their stray capacitance toground.

A liner for electrodes of 1.2 meter length and width of 10 centimetersarea has about 2500 centimeters squared and a no-plasmaelectrode-to-ground capacitance between about 150 picofarads and 400picofarads, yielding a total capacitive reactance of about 27 Ohms to 72Ohms. Therefore, for series resonance the inductor size at 13.56 MHz forsplitting current might be between about 0.3 microhenries and 0.8microhenry. This inductance range—both bottom and top—would scaleroughly inversely with the operating frequency, and inversely with thearea of the electrode which is the product of the length times widthtimes a factor of about 1.5 if no change is made in the dielectricthickness. However, use of higher operating frequency may oblige one touse a thicker dielectric in order to keep its reactance up at anacceptable value. For example, the dielectric thickness might increaseroughly as the square root of the operating frequency, and so thereactance of the liner would increase similarly were the frequency notto change. The inductor value also will tend to increase, roughlylinearly, in size as the gap between liner surface and substrateincreases.

In summary, in example embodiments, the high pressure discharge may bepredominantly resistive in electrical impedance under mostcircumstances. When the liner is added to the high pressure dischargethe reactive impedance is substantially raised which helps to stabilizeand keep equal the power splitting to the electrodes and plasmas. Itshould be noted, as well, that the presence of the liner causes there tobe a minimum reactance for a liner area of 2500 centimeters squared ofabout 7 Ohms for the high pressure discharge.

FIG. 19 shows an example embodiment in which there is an electrode,1901, which is adjacent at least one other electrode, at least one ofwhich is powered, into a recessed area that is along the length of theelectrode. There is gas injected in its middle, 1902, as well as fromsurrounding areas of the electrode, 1903. These gases may be mixturesand may be different or the same composition. After injection the gasesflow adjacent a workpiece surface, 1900, and thence to one or morechannels, 1904, which lead to exhausts from the chamber. Such channelsleading to exhausts in some embodiments may be symmetrical with respectto the electrodes so that the gas flow divides almost equally betweenthe two directions, left and right in the figure. Gases injected fromthe recess, 1905, may be different in composition from gases injectedfrom other areas of the electrode, 1906, that are closer to thesubstrate. In particular, for deposition of silicon oxide or siliconnitride the gas injected in recesses may be oxygen or nitrogen, ormixtures containing these gases along with inert gases.

In FIG. 20 is shown an electrode. 2000, adjacent other electrodes, witha substrate to be processed, 2001, and plasma, 2002, formed between allof these by the application of RF or VHF power to one or moreelectrodes. The gas is injected from the electrode into the spacebetween the electrode and the substrate. Within said electrode is a gasinjection manifold which has an inner channel, 2003, into which gas maybe injected from a supply, 2005, and one or more outer channels. 2004,into which a separately controllable supply of gas, 2006, may beinjected. Gas is injected into the plasma via a row or rows of smallholes, 2007, from each channel to the surface of the electrode. Gas mayconduct within the manifold from one channel to the next throughrestricted connections, 2008, whose cross sectional area for conductionfrom one channel to the next is smaller than that along the length ofeither channel. Once injected into the plasma the gases flow, 2009, awayfrom the center of the electrode just past the edge of the electrodewhere the gas diverts to flow to the exhausts, 2010, via narrow gapsbetween the electrodes. In some embodiments, where amorphous silicon orsome other materials that have properties sensitive to the gas phasecomposition, it may be desirable to maintain the same gas compositionabove the region of the substrate surface where deposition is takingplace. In this case, when one or more gas constituents such as silane ismore strongly depleted than others as the gas flows over the substrate,it is desirable to replenish it while not also injecting more of otherspecies not depleted in the gas, such as hydrogen. In exampleembodiments represented by FIG. 20, the gas mixture fed to the outerchannels, 2004, may be a mixture of gases rich in silane, or depletedgas component for other deposition process, so that the injected gasfrom rows of holes progressively farther from the center becomesincreasingly rich in such depleted constituent as the flow progresses.Using this approach, by putting most enriched gas in the outer channelwe can make the mixture of gases injected progressively more enriched asthe gas moves from the center to the edge of the electrode so that theconcentration of the critical species in the gas phase may be maintainedapproximately constant.

FIG. 21 a shows a schematic of an embodiment of a system that may beused for depositing dielectrics such as silicon oxide or silicon nitrideon substrates having temperatures less than about 200 Celsius. There aretwo or more electrodes, 2100, that are supplied RF or VHF power ofapproximately the same voltage but whose phase may be different. Theseelectrodes are separated from a substrate, 2101, that moves to the rightin the figure. For depositing silicon oxide or other oxides or nitridesgas, 2102, is injected into the gap between the electrodes that mayinclude oxygen or nitrogen or other species for forming thin films onsubstrates. There is a plasma in this gap, 2107, which may in someembodiments have a higher power density and plasma density than theplasma between the electrodes and the substrate for more rapidly andcompletely dissociating this gas to make reactive species before theother gas is injected. A precursor gas for deposition is also injected,2103, into the electrodes which passes into a channel, 2104, and thenthrough small holes, 2105, in the sides of the electrodes facing theother electrode, on its way to the plasma. This precursor gas maycontain silane or other gas containing one or more elements such assilicon, zinc, titanium, aluminum, carbon, indium, ruthenium, tin,molybdenum, gallium, arsenic, phosphorus or tantalum. When the injectedgas reaches the plasma it reacts very quickly with the dissociatedreactive gas species such as oxygen, nitrogen, or other, and may becomefully reacted in the gas phase, so that the resulting compound of thedepositing element from the precursor and the reactive species maydeposit on the substrate. Examples of compounds that may be depositedinclude silicon oxide, titanium dioxide, gallium nitride or siliconnitride. One potential advantage of embodiments of the disclosedinvention is that films of high quality having less incorporatedhydrogen or carbon may be deposited on substrates having lowertemperatures than normal—for example, having temperatures lower than sabout 200 Celsius. This further applies to epitaxial deposition ofsubstances such as gallium nitride where normal substrates may be 600Celsius. In example embodiments, epitaxial deposition may occur onsubstrates having temperatures less than about 600 Celsius. In thiscase, use of electrodes having liners reduces heat absorbed byelectrodes. In fact, liners having two or more layers of dielectricliners, such as quartz or opaque quartz, can be used, thereby greatlyreducing the heat flux to electrodes and facilitating suchplasma-assisted epitaxial deposition. With such multiple layer liners itmay be beneficial to use RF or VHF frequencies above 13.56 MHz so as toreduce the RF impedance of the liners. The width of the electrode, 2100,in some embodiments may be between about 1.5 centimeters and about 15centimeters, because the depositing compound may be depleted from thegas phase rapidly as the gas flows away from the point where theprecursor enters the plasma. The gases, having been injected betweenelectrodes and then after passing under the electrodes divert to passbetween an electrode and the neighboring electrode or divider to theexhaust, 2106. This embodiment and method may produce dielectric andother films of good quality at lower substrate temperatures thanconventional PECVD reactors. Multiple pairs of such electrodes may bearranged with their long sides parallel with gaps between them that arebetween about 5 millimeters and about 15 millimeters.

FIG. 21 b shows a configuration appropriate to some embodiments where itis desired to reduce the plasma power density and pre-dissociation ofspecies prior to mixing of all reactive gases and flow adjacent thesubstrate. The electrodes, 2111, in some embodiments may have adielectric material, 2115, for example with a low dielectric constant,interposed between them and filling much of the space between where gasis introduced. In this way only a modest volume, 2117, remains availablefor plasma and dissociation of feed gases before the bulk gas flowcarries them between electrodes and substrate. Gas may be introducedinto this volume directly, either from the electrode(s) via manifold,2118, and/or from a separately controllable supply, 2114. Gas may alsobe injected from separately controllable supplies 2112 and 2113 into themanifold 2118 that injects gas both to the gap between electrodes 2117and the space between electrodes 2111 and substrate 2119. Once injectedinto this plasma it flows toward the substrate, then betweenelectrode(s) and substrate, and finally in the narrow spaces betweenelectrodes and neighboring elements, 2116, and thence to the exhaustfrom the chamber. Gas injected between electrodes, 2114, may be inertgas, process gas mixture or a separate mixture containing precursorand/or reactive gases.

In FIG. 22 we see a configuration for some embodiments well suited toproviding a flow pattern and velocity for the gas in the plasma whichhas only very slight variation, less than or of order 1%, along thelength of the electrodes and plasma. It may be desirable for good plasmaand process uniformity that the gas flow be highly constant along thelength of the plasma, without much convergence or divergence as the gasflows between the substrate and the electrode. This means the directionof gas flow, for virtually the entire length of the source, should beperpendicular to the long direction of the electrode(s). In someembodiments where gas. 2201, from a separately controllable supply, isinjected into the gap between electrodes through a manifold, 2202, thisshould have a cross sectional area greater than about 1 squarecentimeter in the plane of the figure. This, at the gas pressurespreferred for this invention, between about 100 Pascals and about 5000Pascals, results in a high gas conductance over the length of thismanifold extending almost the entire length of the electrodes, 2206. Insome embodiments there may be multiple parallel gas feeds to thismanifold, distributed along its length, so that the pressure within ishighly constant. The gas then flows through small holes or slots, 2203,and then downward in the figure through the space between electrodes.The combined area of such small holes or slots normal to the flowdirection should be less than the cross sectional area, as shown in thefigure, of the injection manifold from which they issue. In fact, thecombined gas conductances of all such small ducts coming from themanifold should be less than the conductance of the manifold for halfits length. As a consequence the gas pressure in the injection manifoldis nearly constant so that the flow of gas from the small ducts into thegap between electrodes is very nearly independent of the position alongthe length. Once the gas flows between electrodes toward the substrateand then diverts to flow between substrate and electrode, and thenhaving passed the electrode diverts again to flow in the narrow gap,2205, between an electrode and the neighboring element, 2207, which maybe an electrode. The flow in these narrow spaces according to thedisclosed configuration will be effectively in the plane of the figureand independent of the position along the length of the source. Once gashas flowed through such narrow gap, it passes through exhaustaperture(s) into the exhaust manifold, 2204. The gas conductance of suchmanifold should be substantial along the direction parallel to the longdimension of the electrodes so that its cross sectional area in theplane of the figure may be five square centimeters or more. With suchhigh gas conductance the gas pressure along the length of such manifoldwill be nearly constant. To further improve the uniformity and constancyof the gas pressure in the exhaust manifold it is helpful to provide,along the length of this manifold, more than one pump-out port, 2208,from the duct to the vacuum pumps, and they should be distributedsomewhat evenly along the length. It is desirable that ducts connectingsuch pump-outs to the main vacuum line be of equal conductance so thatthe pressures at the pump-out ports are equal.

FIG. 23 shows an example multi-layer structure that may be manufacturedusing example systems and methods according to example embodiments. Forexample, a reactor having multiple PGUs for sequentially depositingdifferent layers may be used, such as the example reactor shown in FIG.13. It will be understood that the number of PGUs for each layer and thenumber of layers to be deposited may be varied depending upon thedesired structure to be formed. In FIG. 23, an example multi-layerstructure is shown consisting of alternating layers of thin films of twomaterials either or both of which might be dielectric, electricallyconducting, or semiconducting. Such a stack might be used for a dichroicoptical filter to transmit a certain wavelength band while it reflectsalmost perfectly other wavelength bands. Another application might besuperlattice structures for optical, photovoltaic, display or electronicapplications. A third application might be for photovoltaic devicesrequiring alternating layers to be doped or undoped. For properfunctionality in many applications such multi-layer structures shouldhave precise and highly uniform thicknesses over most of the area of thesubstrate. For large rectangular substrates this is a very difficulttask and may require the ability to maintain 1% to 2% control andrepeatability of layer thicknesses and compositions. Exampleembodiments, such as those described above, are believed to havesubstantial advantage in fabricating such structures due to theirability to deposit many layers at the same time in the same system onmoving substrates such that these deposits become different layersdeposited at different levels on the substrate (for example, asdescribed in connection with FIG. 13). In FIG. 23 layers alternate inthickness and material type, from layers of material 2301 which arethinner to layers of material 2302 that are thicker. Such layers couldbe alternating layers of transparent dielectric for a dichroic filter.In this case they would in some embodiments have different refractiveindices and probably little absorption of light in the workingwavelength region. Two such materials could be silicon oxide for thethicker layers and titanium dioxide for the thinner layers. Thicknessesin some embodiments might be in the range of 500 to 2000 Angstroms forthe silicon oxide and 200 to 1000 Angstroms for the titanium dioxide. InFIG. 13, the layers of each material as shown are repeatedly the samethroughout the stack, but the layers of each material may actually varyin thickness. In example embodiments, the number of PGUs, power, gasmixture and gas flow may change for subsequent processing stations inthe reactor to achieve different layer thicknesses, properties andcomposition as part of a high throughput sequential deposition process.In example embodiments, the workpiece may be moved by a conveyor underthe different sets of PGUs to deposit the various different sequentiallayers.

Whether the delivery of the AC power into the plasma is done byinductive or capacitive coupling or both the following features (or anycombination thereof) may be provided in example embodiments:

In example embodiments, the elements in the PGU, including electrodes,or groups of windings of coils, as well as dividers, may be much longerthan their width in the direction perpendicular to the gap from theelements to the substrate.

In example embodiments, the gap between the elements of the PGU and thesubstrate may be smaller than the width of the AC powered elements,whether electrodes or group of windings, and such gap may in someembodiments be between about 5 mm and 15 mm.

In example embodiments, the gas flow between the AC powered elements(electrodes or groups of windings of coils) and the substrate may have avery small component of flow velocity parallel to the long direction ofthe elements compared to its component of flow velocity perpendicular tothe long dimension of the elements. The bulk flow of gas between ACpowered elements and the substrate may be largely parallel to thesubstrate and neither convergent or divergent as it flows proximate theAC powered element. The concentrations of species in the gas may begenerally independent of the position along the length of the AC poweredelements or PGUs and easier to scale-up the length of the elements toprocess ever-larger substrates. In order to achieve this parallel,sheet-like flow of gas between elements and substrate, both the gasinjection and gas pumping may be highly uniform along the length of theelements. This may be accomplished with appropriate distribution andpumping manifolds in example embodiments.

In example embodiments, such gas flow may be effectively around each ACpowered element perpendicular to the long direction of the element andthence into the exhaust port proximate that element. Therefore, the gasstream around any AC powered element can be largely confined to thatelement. In case processes are highly sensitive to some gaseous speciesused in one or a group of PGUs an intervening element with only inertgas injected proximate or from it may be used in example embodiments.This may be used to provide gaseous isolation of processing regions eachfrom the other. In consequence, there may be a number of different gasmixtures used so that two or more different processes are performed onone or more substrates simultaneously within the same processing chamberwithout large purged separation or extensive baffling between.

In example embodiments, the AC powered elements may be covered bydielectric or weakly conducting liners or shields. In exampleembodiments, the liners or shields may have modest thermal expansioncoefficients. Such liners may prevent the gas from cooling due tocontact with cold surfaces. This may help maintain constant gaps betweenelectrodes or windings. Such shields or liners may also tend tostabilize the power density uniformity of the plasma in someembodiments.

Example embodiments may also cause plasmas sustained between each ACpowered element and the substrate to be mainly dependent on the powerinjected from that element. This permits largely independent variationof plasma power density proximate the different powered elements, andwhen used along with independence of gas chemistry for each PGU, makespossible substantially independent variation of simultaneous processeson the substrate within different PGUs or processing regions. This canbe used to facilitate and make more economical deposition of multilayerstructures or integrated sequential treatments of substrates.

Although the invention has been described in reference to exampleembodiments it will be appreciated that specific components orconfigurations described with reference to one figure may equally beused when appropriate with a configuration described in another figure.Any description of these examples are not intended to limit theinvention as changes and modifications can be made without departingfrom the spirit or scope of the invention.

What is claimed is:
 1. A method for plasma-based coating of thin filmson a substrate, said method comprising: placing a substrate on a supportwithin a chamber such that a side of said substrate to be coated facesat least one electrode of a plurality of electrodes within said chamber,and a minimum gap between said one electrode and said substrate is lessthan a width of said one electrode, wherein said chamber is connected toa vacuum pump, a gas pressure in said chamber is maintained in a rangeof 50 Pascals to 2000 Pascals, said plurality of electrodes within saidchamber have lengths greater than their widths or heights, and said atleast one electrode has a front side opposite said support for saidsubstrate; maintaining a part of said substrate adjacent said support ata temperature less than 200° C.; providing AC power to at least a firstelectrode of said plurality of electrodes to form a plasma between saidfirst electrode and a second electrode of said plurality of electrodes,and between said first electrode and said substrate providing ionbombardment of said substrate; and injecting a first gas into a spacebetween opposing faces of said first and second electrodes to flowtowards said substrate in the plasma between said first and secondelectrodes so that said gas deposits a thin film on said substrate as itflows adjacent said front side of said at least one electrode withoutrecirculation.
 2. The method of claim 1 wherein said AC power is one ofRF or VHF power.
 3. The method of claim 1 wherein said length of saidone electrode is greater than four times said width of said oneelectrode or said height of said one electrode.
 4. The method of claim 1wherein a minimum gap between any respective one of said plurality ofelectrodes and said substrate on said support is less than the width ofsaid respective electrode.
 5. The method of claim 1 wherein aninter-electrode gap is between 5 mm and 20 mm.
 6. The method of claim 1wherein a flow of mixed gas is around at least one of said plurality ofelectrodes to an exhaust.
 7. The method of claim 1 wherein a first powerdensity in an inter-electrode gap is higher than a second power densitybetween said one electrode and said substrate; and a power ratio betweensaid first power density and said second power density is less than afactor of
 5. 8. The method of claim 1 wherein said first gas comprises acompound of at least one of nitrogen or oxygen; and a second gascontains a silicon compound to form a film with said first gas thatcontains silicon oxynitride or silicon nitride.
 9. The method of claim 1wherein a dielectric film is deposited on said substrate.
 10. The methodof claim 1 wherein a transparent, metal-containing, electricallyconducting film is deposited on said substrate.
 11. A method forplasma-based film deposition of silicon-based materials on a substrate,said method comprising: placing a substrate on a support structure in achamber such that a surface of said substrate to be coated faces afirst, front surface of an electrode positioned within said chamber andforms a volume between, said surfaces, said first front surface of saidelectrode facing said support structure, a minimum gap between saidsurfaces being less than a width of said electrode, said chamber beingconnected to a vacuum pump, and a gas pressure in said chamber beingmaintained at less than 2000 Pascals; maintaining said substrate at atemperature under 200 degrees Celsius; injecting a first reactant gascontaining a non-silicon-based compound such that the first reactant gasflows toward said substrate adjacent a second surface of said electrode;providing AC power to said electrode to form a first plasma byactivating said first gas adjacent said second surface, and further,forming a plasma between the front side of said electrode and saidsubstrate providing ion bombardment of said substrate; and injecting asecond gas into said flowing activated first gas to form a mixed gas,said second gas comprising a silicon-containing compound, and depositinga silicon-based thin film upon the substrate, wherein said mixed gasflows adjacent said front side of said electrode and then to an exhaust.12. The method of claim 11 wherein said AC power is one ofradiofrequency (RF) or very high frequency (VHF) power.
 13. The methodof claim 11 wherein said minimum gap between said first side of saidelectrode and said substrate is between 5 mm and 20 mm.
 14. The methodof claim 11 wherein the flow of said mixed gas is around said electrodeto said exhaust.
 15. The method of claim 11 wherein said first gascomprises a compound of at least one of nitrogen or oxygen, and saidsecond gas contains a silicon compound to form a film with said firstgas that contains silicon oxynitride or silicon nitride.
 16. The methodof claim 11 wherein a dielectric film is deposited on said substrate.17. The method of claim 11 wherein a transparent, metal-containing,electrically conducting film is deposited on said substrate.